使用氧气时，操作人员应站在出气口的侧面，缓慢开启阀门;乙炔瓶必须直立放置，不准卧放。()
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气焊、气割用的新橡皮管在首次使用时，要先把橡皮管内的滑石粉吹干净，以防焊炬内部的通道被堵塞。()
Modern agriculture is criticized as unsustainable because _____.
A. it promotes the erosion of topsoil
B. it cannot provide a long-term planning
C. 300 years is not long enough for the development
D. the lost topsoil is irreplaceable
The sentence "We are trying to think out of the box" (Para, 4) suggests that_____.
A. they will try to find wisdom out of the box
B. they will probe deep into the pools of academy
C. they will break away from the conventions
D. they will pursue their traditional approach
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