若有理数a、b满足ab>0,且a+b<0,则下列说法正确的是 [ ]
A.a,b可能一正一负
B.a,b都是正数
C.a,b都是负数
D.a,b中可能有一个为0
答案:C
Mary is very clever and worth teaching , but her brother is not .Look ,he is now asleep in class .
A.very ; very
B.much; very
C.well; very
D.well;fast
点火时间过迟、混合气过稀或过浓,都将引起发动机冷却系水温()。