如图是四冲程汽油机做功冲程的示意图．汽油燃烧产生高温高压的气体推动活塞向下运动．在活塞向下运动的过程中，汽缸内气体的（   ）（多选）

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 Dear Grandma,

    Thank you for the new shorts. They are cool! It's hot in Beijing. It's sunny too. I can wear my shorts and T-shirt. I have a new jacket. My old jacket is too small. I want to buy a hat. It is fifty yuan. It's too expensive.

   What's the weather like at the farm? Is it warm? How many new ducks are there?

                                                                                                                                                                 Love

                                                                                                                                                                 John

“杯酒释兵权”的故事反映了北宋建立后（    ）