如图所示,滑雪者由静止开始沿斜坡从A点自由滑下,然后在水平面上前进至B点停下。已知斜坡、水平面与滑雪板之间的动摩擦因数都为μ,滑雪者(包括滑雪板)的质量为m.。A、B两点间的水平距离为L。在滑雪者经过AB段运动的过程中,克服摩擦力做的功( )A.大于μmgL B.等于μmgLC.小于μmgL D.以上三种情况都有可能
Paper ____ first ____ about two thousand years ago in China by Cai Lun.( )
A.is; inventingB.is; invented
C.has; inventedD.was; invented
____ noise pollution, and we can live in a quiet environment.( )
Prevent
Preventing
Prevented
To prevent
Your new watch is so nice! When did you buy it?
In October. I ____ it for two months.( )
had
bought
have had
have bought
Linda has ____ to Paris. How can I get in touch with her?
Don't worry. She will call you as soon as she ____ there.( )
been;will get
been;gets
gone;will get
gone;gets
I like the TV program The Reader best. I think we should spend as much time as we can ____ in our spare time.( )
read
to read
reading
reads