单项选择题
If the United States had built more homes for poor people in 1955, the housing problem now in some parts of the country ______ so serious.
单项选择题 It will be warmer and warmer, ______ more and more trees are turning green.
单项选择题 Prisons in the country are short of staff, ______ means prison officers are overworked and underpaid.
单项选择题 I don’t understand ______ he should have done something like that.
