Now the air in our city is ________ than
题型：选择题
问题：
Now the air in our city is ________ than it used to be．Something must be done to stop it．
A．very good
B．much better
C．rather bad
D．even worse
题型：选择题
| 如图所示，AB是一质量为m的均匀细直杆，A端靠在光滑的竖直墙壁上，B端置于水平地面上，杆身与竖直方向夹角为θ，杆与地面的摩擦系数为μ，保持平衡，则此时杆与地面的摩擦力为（ ） A． B． C． D．μmg  |
mgtgθ
mgsinθ