下列运算正确的是[ ]
A．x5+x5=x10
B．x5·x5=x10
C．(x5)5=x10
D．x20÷x2=x10
答案：B
John thinks it won’t be long_________he is ready for his new job.
A．when
B．after
C．before
D．since
安装活塞环时，有文字或记号面朝上，压缩环上下环可互换。
