巷道间距小于（）m的联络巷可以不设防尘供水管路。
A.20
B.30
C.50
D.60
参考答案：C
They are good friends. _____ is no wonder that they know each other so well.[ ]
A. This
B. That
C. There
D. It
什么叫中体？什么叫质粒？细菌质粒有何特性？
