有几个英语问题不太明白 请各位 高手帮我一下

Meanwhile,they should encourage those among us who cannot swim five yards before they are gasping for air 为什么结尾用现在进行时呢 改成efore they gasp for air 不好吗 ？Specially-made lanterns are hung outside each house to help the dead to find their way. 这句用 outsiderAll night long, people dance and sing. In the early morning, the food that had been laid out for the dead is thrown into a river or into the sea as it is considered unlucky for anyone living to eat it 为什么这句用out呢 还有这句为什么用过去完成时不懂