—_____ do you have music?
—I have music on Friday. [ ]
A. Why
B. When
C. What
D. Who
答案:B
计算图所示V形弯曲件的展开长度。(R=40mm)
IP地址块202.120.80.128/26包含了()个主机地址。
A.15
B.31
C.62
D.127