QUES: The quality of a vacuum is indicated by the amount of matter remaining in the system, so that a high quality vacuum is one with very little matter left in it. Vacuum is primarily measured by its absolute pressure, but a complete characterization requires further parameters, such as temperature and chemical composition. One of the most important parameters is the mean free path (MFP) of residual gases, which indicates the average distance that molecules will travel between collisions with each other. As the gas density decreases, the MFP increases, and when the MFP is longer than the chamber, pump, spacecraft, or other objects present, the continuum assumptions of fluid mechanics do not apply. This vacuum state is called high vacuum, and the study of fluid flows in this regime is called particle gas dynamics. The MFP of air at atmospheric pressure is very short, 70 nm, but at 100 mPa (~6997100000000000000♠1×10−3 Torr) the MFP of room temperature air is roughly 100 mm, which is on the order of everyday objects such as vacuum tubes. The Crookes radiometer turns when the MFP is larger than the size of the vanes.

What indicates the quality of residual gases?
What is the answer?
ANS: unanswerable
QUES: Scientists have been studying the impact of climate change and water use. For example, each year more water is diverted from rivers for snowmaking in the ski resorts, the effect of which is yet unknown. Furthermore, the decrease of glaciated areas combined with a succession of winters with lower-than-expected precipitation may have a future impact on the rivers in the Alps as well as an effect on the water availability to the lowlands.

Who have been studying the impact of climate change and water use?
What is the answer?
ANS: Scientists
QUES: The Reformation in Europe officially began in 1517 with Martin Luther (1483–1546) and his 95 Theses. The Reformation greatly changed the Baltic region. Its ideas came quickly to the Livonian Confederation and by the 1520s were widespread. Language, education, religion and politics were transformed. Church services were now conducted in the vernacular instead of in Latin, previously used. During the Livonian War in 1561, northern Estonia submitted to Swedish control. In the 1560s two voivodeships of present-day southern Estonia, Dorpat Voivodeship (Tartu region) and Parnawa Voivodeship (Pärnu region), became the autonomous Duchy of Livonia within the Polish-Lithuanian Commonwealth, under joint control of the Polish Crown and the Grand Duchy. In 1629, mainland Estonia came entirely under Swedish rule. Estonia was administratively divided between the provinces of Estonia in the north and Livonia in southern Estonia and northern Latvia. This division persisted until the early twentieth century.

What was the year of Martin Luther's death?
What is the answer?
ANS:
1546