颅底部横轴位MR扫描，图像前部出现半环形无信号区，可能为（）
A.化学位移伪影
B.金属异物伪影
C.卷褶伪影
D.截断伪影
E.搏动伪影
参考答案：B
The company designed a new car last month and about 500 cars of this type in the factory next month.
A．were produced
B．will produce
C．have been produced
D．will be produced
毒扁豆碱用于青光眼的优点是( )
A．比毛果芸香碱作用强大而且持久
B．毒副作用比毛果芸香碱小
C．水溶液稳定
D．不易引起调节痉挛
E．不会吸收中毒
