— Tom fell off his bike and hurt his arm yesterday.

—           .[ ]

A.Congratulations

B.That's funny

C.All right

D.I'm sorry to hear that

伤寒复发的原因是（）。

A.免疫力低下

B.药物产生耐药性

C.潜伏在胆囊、骨髓、肠系膜淋巴结中的细菌重新繁殖入血

D.血中的细菌未肃清

E.再次感染细菌