——He always appears to _________. ——That's because he's really knowledgeable and experienced.
A:make an effort
B:have a point
C:pull together
D:take place
把下列词语补充完整。
束手____ 千辛____
下列计算中,正确的有( )①am×an=amn;②am+n2=a2m+n;③2anb3×-16abn-1=-13an+1bn+2;④a6÷a3=a2。