— Here is a piece of paper for you! —
题型：选择题
问题：
— Here is a piece of paper for you!
— Oh, thanks. It's for me to write a long letter on. [ ]
A. big enough
B. enough large
C. small enough
D. enough small
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