Some symbiotic relationships are obligate, meaning that both symbionts entirely depend on each other for survival. For example, many lichens consist of fungal and photosynthetic symbionts that cannot live on their own. Others are facultative (optional): they can, but do not have to live with the other organism.
What is an example of an obligate relationship?
lichens


Input: Franco-Prussian War
The casualties were horrible, especially for the attacking Prussian forces. A grand total of 20,163 German troops were killed, wounded or missing in action during the August 18 battle. The French losses were 7,855 killed and wounded along with 4,420 prisoners of war (half of them were wounded) for a total of 12,275. While most of the Prussians fell under the French Chassepot rifles, most French fell under the Prussian Krupp shells. In a breakdown of the casualties, Frossard's II Corps of the Army of the Rhine suffered 621 casualties while inflicting 4,300 casualties on the Prussian First Army under Steinmetz before the Pointe du Jour. The Prussian Guards Infantry Divisions losses were even more staggering with 8,000 casualties out of 18,000 men. The Special Guards Jäger lost 19 officers, a surgeon and 431 men out of a total of 700. The 2nd Guards Infantry Brigade lost 39 officers and 1,076 men. The 3rd Guards Infantry Brigade lost 36 officers and 1,060 men. On the French side, the units holding St. Privat lost more than half their number in the village.

What was the number of French prisoners?
Output: 4,420


Input: Article: Daniel Gralath was the first to combine several jars in parallel into a "battery" to increase the charge storage capacity. Benjamin Franklin investigated the Leyden jar and came to the conclusion that the charge was stored on the glass, not in the water as others had assumed. He also adopted the term "battery", (denoting the increasing of power with a row of similar units as in a battery of cannon), subsequently applied to clusters of electrochemical cells. Leyden jars were later made by coating the inside and outside of jars with metal foil, leaving a space at the mouth to prevent arcing between the foils.[citation needed] The earliest unit of capacitance was the jar, equivalent to about 1.11 nanofarads.

Now answer this question: Why was a gap left at the mouth of Leyden jars?

Output: to prevent arcing between the foils


Article: Strasbourg features a number of prominent parks, of which several are of cultural and historical interest: the Parc de l'Orangerie, laid out as a French garden by André le Nôtre and remodeled as an English garden on behalf of Joséphine de Beauharnais, now displaying noteworthy French gardens, a neo-classical castle and a small zoo; the Parc de la Citadelle, built around impressive remains of the 17th-century fortress erected close to the Rhine by Vauban; the Parc de Pourtalès, laid out in English style around a baroque castle (heavily restored in the 19th century) that now houses a small three-star hotel, and featuring an open-air museum of international contemporary sculpture. The Jardin botanique de l'Université de Strasbourg (botanical garden) was created under the German administration next to the Observatory of Strasbourg, built in 1881, and still owns some greenhouses of those times. The Parc des Contades, although the oldest park of the city, was completely remodeled after World War II. The futuristic Parc des Poteries is an example of European park-conception in the late 1990s. The Jardin des deux Rives, spread over Strasbourg and Kehl on both sides of the Rhine opened in 2004 and is the most extended (60-hectare) park of the agglomeration. The most recent park is Parc du Heyritz (8,7 ha), opened in 2014 along a canal facing the hôpital civil.

Question: What park is built close to the Rhine by Vauban?
Ans: Parc de la Citadelle


Here is a question about this article: The black-body problem was revisited in 1905, when Rayleigh and Jeans (on the one hand) and Einstein (on the other hand) independently proved that classical electromagnetism could never account for the observed spectrum. These proofs are commonly known as the "ultraviolet catastrophe", a name coined by Paul Ehrenfest in 1911. They contributed greatly (along with Einstein's work on the photoelectric effect) to convincing physicists that Planck's postulate of quantized energy levels was more than a mere mathematical formalism. The very first Solvay Conference in 1911 was devoted to "the theory of radiation and quanta". Max Planck received the 1918 Nobel Prize in Physics "in recognition of the services he rendered to the advancement of Physics by his discovery of energy quanta".
What is the answer to this question: When did Paul Ehrenfest come up with the name "ultraviolet catastrophe"?
****
So... 1911


Article: Victoria was physically unprepossessing—she was stout, dowdy and no more than five feet tall—but she succeeded in projecting a grand image. She experienced unpopularity during the first years of her widowhood, but was well liked during the 1880s and 1890s, when she embodied the empire as a benevolent matriarchal figure. Only after the release of her diary and letters did the extent of her political influence become known to the wider public. Biographies of Victoria written before much of the primary material became available, such as Lytton Strachey's Queen Victoria of 1921, are now considered out of date. The biographies written by Elizabeth Longford and Cecil Woodham-Smith, in 1964 and 1972 respectively, are still widely admired. They, and others, conclude that as a person Victoria was emotional, obstinate, honest, and straight-talking.

Question: When were the best biographies of Queen Victoria written?
Ans:
1964 and 1972