A:①②
B:②③
C:③④
D:①④
计算:
(1)﹣t3•(﹣t)4•(﹣t)5;
(2)(b2n)3(b3)4n÷(b5)n;
(3)tm+1•t+(﹣t)2•tm(m为整数);
Mr Li says learning English ______ action, or we will get nothing.
①CH3CH2OH② ③CH3CH2Br④ ⑤ ⑥ ⑦ ⑧ ⑨ ⑩