腰椎牵引时首次牵引重量一般为体重的()
A.10%
B.20%
C.25%
D.50%
E.100%
参考答案:C
— We are sorry we can’t stay with you.
— ________.
A.No, sorry at all
B.I don’t think so
C.Don’t think so
D.That’s all right
为了更可靠地消除直流平均环流,可采用()。