When a magnetic compass is not in use for a prolonged period of time it should().
A. be shielded from direct sunlight
B. be locked into a constant heading
C. have any air bubbles replaced with nitrogen
D. have the compensating magnets removed
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抽样调查就是成为()的途径与手段。
A. “由部分认识总体”
B. “由总体认识部分”
C. “有理论认识现实”
D. “由现实认识理论&rdquo
任一零件可以有多个尺寸参与装配尺寸链。
A. 正确
B. 错误