下列有机硫化物中，（）可作为天然气的加臭剂。
A.乙硫醇
B.甲硫醚
C.甲硫醇
D.硫化碳
参考答案：C
—Has your brother found an apartment yet?
—No, he's still living in a room downtown, but I ________ him look.
A．help
B．have helped
C．am helping
D．helped
上述结构使细菌具有致育性的为
A．茭膜B．鞭毛C．普通菌毛D．性菌毛E．芽孢
