根据短文内容，判断下列各句正误。
      Hong Kong has about forty public beaches. Some of them are very famous around the world. People can go there for a swim. You can go to them by bus. To go to some beaches you must take a boat.
    You will swim there without danger if you remember these instructions:
    Never swim alone.
    Never go out in a boat if you cannot swim.
    Never swim after a meal or when you feel hungry or tired.
    Don't stay in the water too long.
    Remember: A red flag means that it is dangerous for anybody to go into the water. A blue flag means that it is dangerous for children.

小李用下面的方法测量某种液体的密度。首先用调好的天平测出盛有适量水的烧杯A的总质量为60g，然后用细线拴着一个小球，将其浸没在烧杯A内的水中，不触碰烧杯的底和壁，天平平衡后如图甲所示，此时天平的测量值为____ g。接着他用天平测出盛有适量待测液体的烧杯B的总质量为60g，再用细线拴着擦干后的同一个小球浸没在烧杯B内的液体中，不触碰烧杯的底和壁，天平平衡后如图乙所示。则待测液体的密度为____ kg/m³。

顾炎武在（日知录）中说：“有亡国，有亡天下……易姓改号，谓之亡国，仁义充塞，而至于率兽食人，人将相食，谓之亡天下……亡国者，肉食者谋之，保天下者，匹夫之贱，必有责焉耳矣”。下列历史事件中符合“亡天下”含义的是（  ）