观测四等网时，既经济又符合精度要求的接收机是（）.
A.单频机
B.双频机
C.三频机
D.四频机
参考答案：A
把下面句子补充完整。
（1）风一更，雪一更，____________，____________。
（2）人要做有用的人，不要做____________，而_____________________________。
It seems that many people here just need to talk, so I am finding that my job is not limited ________ a
nurse. [ ]
A. in being
B. for being
C. to be
D. to being
