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