There are a number of (reason) why population (is concentrated) in the regions, but the wide variety and (availability) of animal and vegetable life may be (the most important).

单项选择题(After) the (development) (of) the steam engine by James Watt in the late 1700s, the Industrial Revolution progressed (forward) rapidly.

单项选择题(Economist) Adam Smith (published) his book The Wealth of Nations in 1776, (a year) also (notably) for the Declaration of Independence.