桥枕码放时应下边架空,离开地面()以上。
A、20cm
B、30cm
C、40cm
D、50cm
参考答案:B
起重机实际允许的()称为起重量。
What does the passage mainly discuss
A.Why historical archaeology was first developed.
B.How the methods and purpose of historical archaeology have changed.
C.The contributions architects make to historical archaeology.
D.The attitude of professional archaeologists toward historical archaeology.