中度精神发育迟滞的智商为（）
A.40~55
B.35~49
C.30~5O
D.20~40
E.24~39
参考答案：B
已知函数f(x)＝2x，x∈R.当m取何值时方程|f(x)－2|＝m有一个解？两个解？
—Is your home far from school?
—No. It's only _______ walk. [ ]
A. ten-minute's
B. ten minutes'
C. ten minutes
D. ten-minute
