双头螺柱连接适用于（）场合。
A.厚连接件通孔
B.厚连接件不通孔
C.薄连接件通孔
D.薄连接件不通孔
参考答案：B
处方开具当日有效，特殊情况下可以延长有效期，但有效期最长不得超过（）。
-- I had a really nice weekend on the beach.
-- __________.
A．Oh, that's very nice of you.
B．Congratulations
C．It's a pleasure.
D．I' m glad to hear that.
