焊接操作机械主要用于支承焊接件，并使它完成一定的运动，以便使焊接处于有利的焊接位置
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What is the purpose of the intake/exhaust valves in a diesel engine? （）
A. They regulate the combustion cycle
B. They supply cooling water
C. They synchronize the ignition spark
D. They supply and regulate the lubricant flow
Two short blasts of the whistle have all of the following meanings except（）.
A. I intend to meet you starboard to starboard
B. I do not intend to hold course and speed
C. I intend to overtake you on your port side
D. I intend to alter my course to port
由于可转换债券具有可转换股票这一优越条件，所以其发行利率较普通债券高。
A. 正确
B. 错误
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