There are four seasons in a year in Canada. They are spring, summer, autumn and winter. In spring, the weather is warm and sunny. I like to fly kites. In summer, it's hot. I like to swim. I often wear a pair of glasses and a hat. In autumn, it's always cool. I like to go to the park and ride down the street with my friends. In winter, it's cold and snowy. I like to go outside to skate and ski with my friends. Sometimes we make a big snowman, and then we dance and sing around it.

如图所示的实线为汽缸内一定质量的理想气体由状态1到状态2的变化曲线，不考虑气体的分子势能则整个过程中汽缸内气体的内能（   ）

下列对国际日期变更线的叙述，正确的是(       )

“笑气”（N₂O）在医学上曾被用作麻醉剂，其中N元素的化合价是（）