水资源又是一种有限的资源,我国在水资源方面面临着哪三大威胁?
参考答案:
(1)洪水威胁;
(2)干旱缺水威胁;
(3)水环境恶化威胁;
加工齿轮这样的盘类零件在精车时应按照()的加工原则安排加工顺序。
A、先内后外
B、先外后内
C、基准后行
D、先精后粗
One day while Mr. King was working, he had a/an():his left leg was badly injured.
A.business
B.accident
C.matter
D.event