The word "off-limit" in the passage may mean
A. off-set
B. off-state
C. within limits
D. beyond the limit
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According to the passage, it is recommended that the heat exchanger side be cleaned by
A. flushing with chemical solvent without being dismantled
B. brushing mechanically after being disassembled
C. flushing with flesh water only
D. flushing with clean oil only
为了满足工作要求，活塞销的材料一般选用______并经渗碳、淬火和低温回火处理。I、低碳钢(15钢)，II、中碳钢(35钢)，III、合金调质钢，IV、滚动轴承钢(GCr15)，V、合金渗碳钢(20Cr)
A. I+II+V
B. I+V
C. II+V
D. I+III+V
The desirable properties or a marine fuel oil should include_______.
A. high flash point and high viscosity
B. low flash point and high viscosity
C. low heating value and high sulphur content
D. high heating value and low sulphur content
活塞顶部烧蚀可采用_______进行测量
A. 塞尺
B. 深度游标卡尺
C. 测微尺
D. 样板和塞尺
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