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【简答题】
在 SQL 语句中空值用 ________ 表示。 在 SQL SELECT 语句中可以对查询结果进行排序,默认是 ________ 。 在 SELECT 查询中,若要消除重复行,应使用关键字 _____________ 。
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皮皮学刷刷变学霸
举一反三
【判断题】Like the gate valves, a ball valve lifts the flow-control device out of the process stream.
A.
正确
B.
错误
【单选题】Which of the following valves is not belonging to the pressure valves?
A.
relief valve
B.
reducing valves
C.
sequence valves
D.
restrictors
【单选题】In comparison to exhaust valves, intake valves of diesel engines may be fabricated from low alloy steels because _____.
A.
the beveled edges of the intake valves provide for serf-centering during seating
B.
intake valves utilize stellite-coated valve seat inserts which reduce wear
C.
the volume of air passing through intake valves is less than the volume of air passing through exhaust valves
D.
intake valves are less affected to the corrosive action of exhaust gases
【判断题】When compared to gate valves, globe valves have a much greater pressure drop across the valve.
A.
正确
B.
错误
【单选题】患者女性,50 岁,因咳嗽、咳痰、尿少、呼吸困难
A.
，既往有风湿性心脏病二尖瓣狭窄、心力衰竭。医生考虑患者有急性左心衰，其咳嗽、咳痰的性质是（ ）
B.
白色浆液样痰
C.
偶尔咳嗽，咳粉红色泡沫样痰
D.
频频咳嗽，咳大量粉红色泡沫样痰
E.
偶尔咳嗽，咳白色泡沫状痰
F.
痰中带血丝
【判断题】A block valves is any valve that is intended to block flow; also called an isolation valve. The term generally refers to gate valves
A.
正确
B.
错误
【单选题】Gibson Valves produces cast bronze valves on an assembly line. If 1600 valves are produced in an 8-hour shift, the productivity of the line is
A.
2 valves/hr
B.
40 valves/hr
C.
80 valves/hr
D.
200 valves/hr
E.
1600 valves/hr
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