对备用离心泵盘车可以起到的作用是（）
A、防止对轮松动
B、防止泵漏油
C、预防轴变形
D、泵体无杂音
参考答案：C
The wide spread of super hybrid rice around the world ______ the lives of millions and millions of people suffering from hunger to a great level.
A．has improved
B．is improving
C．improved
D．has been improving
聚乙烯搅拌时间为（）
