During a typhoon, you should do your best to     1    . It is also important that you stay inside. If you have to go outside, always exit using the stairs. When you are out,     2    trees, large signs and light poles. Remember to     3    what is going on. Pay attention to news updates to confirm whether the danger is gone. These tips will help keep you safe and sound     4    a typhoon.

There are     1     of water pollution. Large amounts of     2     poison the water after they enter water bodies. Moreover，animal and human waste pollutes the water. Water pollution is also caused by poisonous chemicals     3    .