洗涤红细胞抽检频率（袋／月）是（）。
A.2袋
B.3袋
C.4袋
D.5袋
E.6袋
参考答案：C
—Shall we go and have a picnic at the weekend?
—__________.The weather forecasts say there might be a cold front by then.
A．Why not
B．We can wait
C．No,let’s not
D．It depends
