机电一体化中的滚球丝杠副的使用寿命一般比滑动丝杠要高（）倍。
B.2-3
B.3-4
C.4-5
D.5-6
参考答案：D
---Do you know if he ___to our party?
---I think he will if he ___free tomorrow.
A．comes; is
B．comes; will be
C．will come; is
D．will come； will be
一首容量为30M的普通CD歌曲，压缩成MP3格式后容量大约为（）。
A.1M以内
B.2M-3M
C.10M-12M
D.15M-20M
