投标有效期为从招标文件规定的投标截止之日起到完成评标和招标人与中标人签订合同的()
A.30至200天
B.40至200天
C.30至180天
D.40至180天
参考答案:C
He doesn't do his homework _____, though he has _____.[ ]
A. carefully enough , enough time
B. enough carelessly, time enough
C. carelessly enough, enough time
D. enough carefully,enough time
质量为m的小球A,在光滑的水平面上以速度v0与质最为3m的静止小球B发生正碰,碰撞后A球的速度大小变为原来的1/3,则碰后小球B的速度大小可能为( )
A.2v09
B.v03
C.2v03
D.4v09