船舶安全检查的工作是由（）执行。
A．船长、轮机长
B．公司机务人员
C．船检验船师
D．海事局检查官员
参考答案：D
I think _______ a foreign language is not easy. You should _______ it often. [ ]
A. to learn; to practice
B. learning; practice
C. learn; practicing
D. learns; to practice
