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單項(xiàng)選擇題

The exhaust valve is opened at about the same time （） the air inlet ports are opened.

A.before
B.after
C.when
D.until

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When entering a foam injected space （） breathing apparatus.

A.put out
B.put on
C.take off
D.take in

單項(xiàng)選擇題

The exhaust ports are located around the lower part of the cylinder liner, （）the products of combustion are driven by scavenging air.

A.in which
B.by which
C.through which
D.from which