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R&D

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卷扬机上的钢丝绳（）即应报废。

A. 磨损或腐蚀程度超过钢丝直径20%时
B. 磨损或腐蚀程度低于过钢丝直径20%时
C. 磨损或腐蚀程度低于钢丝直径40%时
D. 在使用过程中断丝数目迅速增加时

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采煤机端部斜切式进刀法如何操作？

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钢丝的磨损或腐蚀程度（）即应报废。

A. 低于钢丝直径20%时
B. 达到或超过钢丝直径20%时
C. 低于钢丝直径40%时
D. 达到或超过钢丝直径40%时

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You own a table called EMPLOYEES with this table structure: EMPLOYEE_ID NUMBER Primary Key FIRST_NAME VARCHAR2(25) LAST_NAME VARCHAR2(25) HIRE_DATE DATE What happens when you execute this DELETE statement? DELETE employees; （）

A. You get an error because of a primary key violation.
B. The data and structure of the EMPLOYEES table are deleted.
C. The data in the EMPLOYEES table is deleted but not the structure.
D. You get an error because the statement is not syntactically correct.

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