关于滤泡性淋巴瘤的叙述，正确的说法是（）

A.心脏易受侵犯

B.对化疗反应好，但不能治愈

C.来源于B细胞

D.发生在生发中心的淋巴瘤

E.病程长，反复复发或转成侵袭性

---Sir, I’m terribly sorry for not having handed in my homework on time, but I have been very busy all these days.

---No excuse for it, but I          drop it this time.

A．might

B．can

C．should

D．must