短命植物与类短命植物一般分布在苔原。( )
参考答案：错
He opened his mouth as if ________ something.[ ]
A. to say
B. say
C. saying
D. to be said
参与经典途径激活补体的是（）。
A.IgE
B.LPS
C.IgD
D.IgA
E.IgM
