中国城市化初始阶段的资金积累主要来自（）
A. 农业
B. 工业
C. 第三产业
D. 三资企业
管涵顶面填土厚度，必须大于（）方能上压路机。
A. 30cm
B. 40cm
C. 50cm
D. 60cm
All of the following are distress signals under the Rules EXCEPT（）.
A. a green star signal
B. orange-colored smoke
C. red flares
D. the repeated raising and lowering of outstretched arm
The error in a magnetic compass caused by the vessel’s magnetism is called（）.
A. variation
B. deviation
C. compass error
D. bearing error
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