题目

A recent survey has demonstrated that a large number of victims during the COVID­19 outbreak ________, if they had worn masks. A . should have been saved B . must have been saved C . need have been saved D . could have been saved 答案：D下列四种调查：①调查某班学生的身高情况；②调查某城市的空气质量；③调查某风景区全年的游客流量；④调查某批汽车的抗撞击能力．其中适合用全面调查方式的是（　　）① B．② C．③ D．④