非致病性微生物包括不产毒霉菌、酵母（）。

A.沙门菌

B.非致病菌

C.低致病菌

D.混合杂菌

E.埃希菌属

They think wearing their own clothes _______ good for their studies. [ ]

A．are

B．do

C．does

D．is