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.
单项选择题 They took ______ measures to prevent poisonous gases from escaping in the chemical plant.
单项选择题 They haven’t decided ______ the microscope themselves or buy one from the United States.
