线材产品最有利于拉拔的金相组织是（）。
A.索氏体
B.马氏体
C.渗碳体
D.贝氏体
参考答案：A
I think students _____ to do homework with friends.
A．should allow
B．should be allowed
C．were allowed
D．must be allowing
什么是苗木日灼伤？
