人类有组织的活动基本分为两种类型,一类是作业,另一类是( )。
A.工作B.事业C.任务D.项目
参考答案:D
Most parents encourage their children to take an active part in social events, ______ those events do not interfere with their studies.
A.concerning
B.until
C.unless
D.provided
当流感病毒流行时,给老人和小孩注射疫苗是为了切断传播途径。[ ]