---Poor Tom! He will have to work all the next month.

---Luckily, ___ the basketball games are held.

A．except

B．except that

C．except when

D．except for

与 * * 毛滴虫致病有关的因素有（）.

A.虫株毒力

B.外界环境

C.宿主生理状态

D.宿主卫生习惯

E.致病菌的协同作用