当下列程序执行时，其输出结果是（）。
A、2k
B、7k
C、-7k
D、-3k
参考答案：B
The rich only ____ themselves in making money and had no eyes for the needs and welfare of their workers. [ ]
A. devoted
B. occupied
C. enjoyed
D. concerned
顶管法顶进长度超过（）应有预防缺氧，窒息的措施。
A、20m
B、30m
C、40m
D、50m
