决定行业进入障碍大小的因素有（）。
A.规模经济
B.产品差异化
C.资金需求
D.销售渠道
E.转换成本
参考答案：A, B, C, D, E
He’s so ill that his father has to send for _______ doctor.
A．one
B．some
C．a
D．the
My brother has changed a lot. He used to be ______, but now he is tall. [ ]
A. short
B. thin
C. pretty
D. heavy
