______a hot summer day, people don't like to go out.
A:At
B:In
C:On
D:Of
小明用20N的水平推力匀速直线推动放在水平地面上的课桌,则课桌受到地面对他的摩擦力大小为 ____N;小明将椅子上的书包放在课桌内,把课桌沿原线路用水平力匀速推回的过程中,则推力大小将 ____20N(填“大于”“等于”“小于”)
一 What did Danny do yesterday?
一 He took part in the meeting.
—I'm afraid I can't travel with you.—Don't worry. We'll going on vacation until you're better.
下列句子的修改不正确的一项是( )