富含蛋白质的食物在烧焦时最容易产生（）和多环芳烃。
查看答案
发动机点火提前角越大，发动机燃烧越完全
A. 正确
B. 错误
Tensile stress is a result of two forces acting in（）.
A. opposite directions on the same line，tending to pull the material apart
B. opposite directions on the same line，tending to compress the object
C. opposite directions along parallel lines
D. the same direction along parallel line
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