When you come into the exhibition hall，you can see a large board with a notice on it，saying visitors__________not to touch the exhibits.

A．will request

B．request

C．are requesting

D．are requested

庆大霉素对下列何种感染无效（）

A.大肠埃希菌致尿路感染

B.肠球菌心内膜炎

C.结核性脑膜炎

D.革兰阴性菌感染的败血症

E.口服用于肠道感染或肠道术前准备