穆罕默德之后是阿拉伯历史上的四大哈里发时期，四大哈里发是阿卜·伯克尔、欧麦尔、奥斯曼和（）
参考答案：阿里
It is ______ that he has been addicted to the drugs and has difficulty quitting it.
[ ]
A. obviously
B. apparently
C. possibly
D. likely
用户充值或消费后可以累积积分，请问积分由哪个系统模块负责管理（）
A.计费
B.营业
C.账管
D.账处
