香草兰是一种名贵的多年生热带藤本香料植物，引种到本地，在冬天不能很好生长而死亡，主要原因可能是（　　）

A．养料不足

B．温度低了

C．水分太少了

D．阳光不足

---  ________ have you kept the book ?

--- Since last Month. I ________ return it to the library today or I can’t borrow one next time.

A．How often; must

B．How long; have to

C．How soon; have to

D．When; must