There are a lot of students in the class
题型：选择题
问题：
There are a lot of students in the classroom. Some are reading and some are _____.[ ]
A. write
B. writting
C. written
D. writing
题型：选择题
一矩形截面外伸木梁如图所示。设截面的高与宽之比为h/b=2，木材的许可弯曲正应力[σ]=10MPa，许用切应力[τ]=2MPa，已知F1=40kN，F2=15kN，l=0.6m。该梁的最小宽度b为（）mm。
A．87.7
B．96.8
C．100
D．245