单项选择题
The professor found himself constantly （）the question: "How could anyone do these things"
A．presiding B．poring C．pondering D．presuming
单项选择题 More than 85 percent of French Canada's population speaks French as a mother tongue and （）to the Roman Catholic faith.
单项选择题 As visiting scholars, they willingly （）to the customs of the country they live in.
单项选择题 We find that some birds （）twice a year between hot and cold countries.
