危险化学品机动车发生事故时要首先向单位领导报告。
参考答案:错
He tried his best to solve the problem,________ difficult it was.
A.however
B.no matter
C.whatever
D.although
大地水准面上任意一点的正高等于______。
A.大地高 B.常数0 C.随机变化量 D.高程异常