有一条导线的电阻为R1，现将它对折扭在一起后电阻为R2，则：[ ]
A.R1 = R2
B.R1＞R2
C.R1＜R2
D.不能确定
答案：B
_____________ all the seats were full, he had no choice but to stand up.
A．For
B．As
C．Though
D．Unless
试区别微生物的拮抗关系和互生关系及其在污水生物处理中的应用。
