Waste paper shouldn't        everywhere .It's our duty to keep our city clean.[ ]

A. be thrown                    

B. throw

C. is thrown                      

D. are thrown

非流行期间流行性脑脊髓膜炎的主要传染源是

A．患者

B．带菌者

C．隐性感染者

D．慢性感染者

E．带菌动物