More than a dozen students in that school ______ abroad to study medicine last year. [ ]

A. sent

B. were sent

C. had sent

D. had been sent

各级网管维护中心负责对用户口令、操作权限的管理，（）

A.账号口令可交叉使用

B.任何人都可用任何账号

C.各类设备与系统应设定各级操作权限和口令

D.操作人员只可使用权限内的操作，用户账号及口令不可泄露给无关人员