—Have you ever visited the Water Cube?

—Yes. When I served as a volunteer in Beijing, I      it twice.

A．have visited

B．visited

C．had visited

D．had been visiting

下列药物中，对纤维化病灶中结核杆菌也有效的是

A．对氨水杨酸

B．链霉素

C．妥布霉素

D．庆大霉素

E．异烟肼