To save time, many Americans buy foods which can be quickly made ready for the table. On holidays, families enjoy delicious meals. For example, on Thanksgiving Day, the fourth Thursday in November, family members get together for a turkey dinner with pumpkin pie(南瓜派).

    People can easily find fast food chains(连锁店),such as McDonalds' and KFC, in most of the big cities in the world.

    These years, many people have taken more and more care of their health while eating. They come to know eating too much meat will make them overweight. Many of them are also worried about food addictives(添加剂). Some of them may be harmful to the body.

国家一级保护动物中具有嗜盐特性的是（    ）

 请用数字和化学符号填空：

（1）2个磷原子　____ ；

（2）硝酸根离子　____ ；

（3）人体中含量最多的金属元素____ ；

（4）氦气　____ ．