下列各式中①a;②b+1;③a2;④a2+3;⑤x2-1;⑥x2+2x+1,一定是二次根式的有( )个.
春季植树时,移栽的树苗常被剪去部分枝叶,主要原因是( )
若a= ∫02 x2dx,b= ∫02 x3dx,c= ∫02 sinxdx,则a,b,c从小到大的顺序为____.
— Sorry, I didn't pass the exam, and then what should I do?
—I think perhaps you should be careful next time.