运输问题有（）情况。
A.需求量等于供应量
B.求量波动很大，供应量波动很小
C.供应量动很大，需求量波动很小
D.需求量不等于供应量
参考答案：A, D
The student asked her professor if he would have gone on the space ship he did know earlier.
A．if he knew
B．if he knows
C．he had known
D．had he known
电缆标石的用途是什么？
