肺炎链球菌的致病力主要来源于（）

A.杀白细胞素

B.血浆凝固酶

C.外毒素

D.荚膜侵袭力

E.内毒素

When the school bus arrived at the zoo, the bus door ______ open and all the children rushed out.

A．shocked

B．destroyed

C．attacked

D．burst