Exercise 2: sample answer

The explanation says that the cold, wet year of 1816, which followed a huge volcanic eruption in 1815 (check), ruined harvests and left horses short of feed, so a horseless vehicle looked attractive and Drais built his machine soon after. It is plausible and often repeated, but it is an inference rather than something Drais is known to have said, so it should be stated cautiously: "it may be that", not "because" (check).