题干
My neighbours used to give me a hand in time of trouble, was very kind of them.
A：who
B：that
C：which
D：whom
答案(点此获取答案解析）
C
My neighbours used to give me a hand in time of trouble, was very kind of them.
A：who
B：that
C：which
D：whom
N2O4 △H<0，如把烧瓶置于100℃的沸水中，则下列几项性质中：①颜色 ②平均分子量 ③质量 ④压强 ⑤密度，其中不会改变的是