在水库的平静水面上，某同学坐在航行的游艇内，若说他是静止的，则所选择的参照物是：

在方格纸上画出下面图形的轴对称图形．

SO₂（g）+NH₃•H₂O（aq）=NH₄HSO₃（aq）△H₁=a kJ•mol^﹣1

NH₃•H₂O（aq）+NH₄HSO₃（aq）=（NH₄）₂SO₃（aq）+H₂O（l）△H₂=b kJ•mol^﹣1

2（NH₄）₂SO₃（aq）+O₂（g）=2（NH₄）₂SO₄（aq）△H₃=c kJ•mol^﹣1

    If you go to fast food restaurant, you can see a lot of teenagers. Today,1teenagers are  2 because of their favorite food. Most teenagers 3junk food 4 a lot of fat, salt and sugar.

    5 bad eating habits are more than junk food. We find many teenagers eat6 Some don't have 7 before they go to school. During the day, some don't 8a proper meal for lunch. In a survey 9 one school, scientists found that over 65% of the students didn't have 10 healthy diet.

    Parents today also 11 about their children's diet. Some doctors give the following 12

    Teenagers shouldn't eat 13 junk food .Teenagers shouldn't eat food with much14 Salt can cause high blood pressure in the future.

Teenagers should eat food without much fat, oil and sugar.

    Teenagers15 to eat some fruits and vegetables every day. Fruits and vegetables are rich in vitamins and they have little fat.