Dear Mr.Brown,

I am sorry to t__小题1:_ you my mother is ill.She c_小题2:day and night .She does not l_小题3:_down and have a rest .My father is not in .He w_小题4:_to Beijing last week. My mother can not look after h _小题5:. The doctor gives her some ___小题6:( 建议).she should stay in bed and _小题7:_(服用) some medicine .So I have to take c_小题8:_of her._ 小题9:_ (可以)I  ask for a day’s  leave?

Thank  you.

Yours  s__小题10:___,

Tom

自身免疫病产生的原因是（）

A.人体免疫系统对病原菌的免疫反应

B.人体免疫系统对过敏原的反应

C.人体免疫系统对人体正常组织细胞的免疫反应

D.自身免疫功能不足引起的