Germs are very small living things. They are so small that we cannot see them unless we use a microscope. They are found in all kinds of places, all over the world. There are four main types of germs that they can invade (侵入) plants, animals and people, and sometimes they can make us sick.

Bacteria (細(xì)菌) live just about everywhere on earth. Not all bacteria are bad. Some of them are good for our bodies. They help us keep things in balance. Good bacteria live in our bodies and help us use the nutrients in the food we eat and make waste from what's left over. We couldn't make the most of a healthy meal without these important helper germs! On the other hand, there are several types of bad bacteria, including those that cause sore throats.

Viruses (病毒) need a host to keep living. They need to be inside a place of a living plant or animal, including humans, or even inside a bacterium! Whatever a virus lives in is called its host. Once a virus finds the perfect host, the goal is to reproduce and spread. Viruses are pretty tricky because they can change quickly to fit a new environment. When viruses get inside people's bodies, they can spread and make people sick.

Fungi (真菌) are kind of like plants. Unlike other plants, fungi cannot make their own food from soil, water, and air. Fungi love warm and wet places. Most fungi are harmless. The kind that can grow on your skin can be treated. It probably won't hurt you. But it really makes you uncomfortable!

Protozoa (原生動物) are extremely small. Most of them live in water. Some protozoa actually eat bacteria and they are good because they also eat the waste of other small living things. Some protozoa are bad, and they live off of other living things, sometimes humans. For example, if a person drinks unclean water, protozoa may cause health problems.

1.Are germs small?

____________________

2.How many germs are mentioned in the passage?

____________________

3.Why can viruses change quickly?

____________________

4.Where do fungi love to stay?

____________________

5.What does the passage mainly talk about?

____________________

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