This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.

Q: Most migrations begin with the birds starting off in a broad front. Often, this front narrows into one or more preferred routes termed flyways. These routes typically follow mountain ranges or coastlines, sometimes rivers, and may take advantage of updrafts and other wind patterns or avoid geographical barriers such as large stretches of open water. The specific routes may be genetically programmed or learned to varying degrees. The routes taken on forward and return migration are often different. A common pattern in North America is clockwise migration, where birds flying North tend to be further West, and flying South tend to shift Eastwards.

A: How do most migrations begin?
****
Q: The two largest metropolitan areas have subway systems: Lisbon Metro and Metro Sul do Tejo in the Lisbon Metropolitan Area and Porto Metro in the Porto Metropolitan Area, each with more than 35 km (22 mi) of lines. In Portugal, Lisbon tram services have been supplied by the Companhia de Carris de Ferro de Lisboa (Carris), for over a century. In Porto, a tram network, of which only a tourist line on the shores of the Douro remain, began construction on 12 September 1895 (a first for the Iberian Peninsula). All major cities and towns have their own local urban transport network, as well as taxi services.

A: What are the two subway systems in Portugal?
****
Q: On the shores of the strait, in 1701, the French officer Antoine de la Mothe Cadillac, along with fifty-one French people and French Canadians, founded a settlement called Fort Pontchartrain du Détroit, naming it after Louis Phélypeaux, comte de Pontchartrain, Minister of Marine under Louis XIV. France offered free land to colonists to attract families to Detroit; when it reached a total population of 800 in 1765, it was the largest city between Montreal and New Orleans, both also French settlements. By 1773, the population of Detroit was 1,400. By 1778, its population was up to 2,144 and it was the third-largest city in the Province of Quebec.

A:
What was Detroit's population in 1773?
****