宇宙是由大量不同层次的星系构成的 其中太阳是一颗____， （选填“恒星”、“行星”或“卫星”）；如图所示，我们在一只气球上画一些小圆点，充气使气球不断膨胀，观察此过程中各个小圆点之间的距离变化，来模拟____。

There are many trees on ____ side of the street.

康熙帝临终前用“立遗诏”的方法解决皇帝继承问题，后来传位于第四子胤禛(即后来的雍正帝)。康熙这种做法明显破坏了中国古代的（   ）

选词填空。

excited, skill, may, they, without, but, include, part

    American teenagers(青少年)enjoy doing part-time jobs．They think it's an important____of growing up．They can learn some important____by doing part-time jobs and they can also make some money in this way．
    American teenagers usually begin to do part-time jobs at the age of 14．On weekdays，they____go to work a few hours a week after school．They usually work for longer at weekends．
    In summer,American teenagers are____if they find part—time jobs at camps or swimming pools．These jobs can bring____much fun．
    Some difficult jobs____teaching， nursing and police work．____these jobs can be helpful for their future．When they grow up，the students with work experience are more likely (可能的)to be successful than those____work experience．

把生锈的铁钉放入足量的稀盐酸中，刚开始出现的现象是____，其反应的化学方程式是____，一段时间后又有气泡放出其原因用化学方程式表示为____．