检索经济统计数字方面的资料应查找哪类工具书（）。
A. 文摘
B. 题录
C. 学位论文
D. 年鉴
If sludge accumulates on the underside of a diesel engine piston, it will（）
A. cause blow-by
B. chemically attack the piston skirt
C. form an emulsion of lube oil and water
D. raise the piston temperature
A star is observed at lower transit. The line of position derived from this sight is（）.
A. on the prime vertical
B. a latitude line
C. a longitude line
D. of no special significance
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