Being a teacher always encouraging students to think for themselves, I won't tell them answers until they __________ on a math problem for more than an hour.

A．have worked

B．will have worked

C．will have been working

D．had worked

与巴尔干地方性肾病有关的是（）

A．赭曲霉毒素

B．黄曲霉毒素

C．展青霉毒素

D．T-2毒素

E．伏马菌素