concave和convex
2009上海市驾驶员地图、上海市郊地图、高速公路图下载
contract，就是“合同”。那contraction呢？
Back purge occurs whenever a vehicle’s fuel tank temperature decreases. The fuel tank pressure decreases due to a thermal contraction of the gas phase, and due to the decrease in the vapor pressure of the fuel in the tank. The decrease in tank pressure causes some air to flow back into the tank through the canister. This condition results in back-purge.
contraction的意思是“收缩”，竟然和contract一点关系也没有，要特别记一下！
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