—You look unhappy .  What’s wrong ?

—I find ____ difficult ______on well with my classmates

A．it; to get

B．it ; getting

C．that ; to get

D．that ; getting

16Mn钢中的Mn的含量（）。

A.≤1.0%

B.≤1.5%

C.≤2.0%

D.≤2.5%