地球上最大的地震带是（）
A、欧亚地震带
B、环太平洋地震带
C、海岭地震带
D、印度洋地震带
参考答案：B
Large quantities of information, as well as some timely help _____ since the organization was built .
A．has offered
B．had been offered
C．have been offered
D．is offered
已知R2+有b个中子，核外有a个电子，表示R原子符号正确的是（ ）
A．abR
B．a-2a+b-2R
C．a+2a+b+2R
D．a+ba-2R
