It has been proved that hard leads to success.
A.work
B.works
C.worked
D.working
答案:D
在生理情况下,皮质醇每天平均分泌量约为()
A.5mg
B.25mg
C.45mg
D.65mg
E.85mg
机械密封的特点是()。
A.摩擦力大
B.寿命短
C.不漏泄