Read the passage and complete the tasks. 阅读短文，完成任务。
The journey of wastewater
From the toilet back to us
When you flush the toilet or take a shower, the water goes down the drain (下水道). But then what happens? Does it go directly into the rivers or the sea? No. The wastewater needs special treatment to make it clean and usable again. Let's follow the journey of wastewater.
Once wastewater goes down the drain, it enters a sewer pipe underground. The pipe takes the wastewater to a sewage treatment plant. The first step of the sewage treatment process is to remove large objects from the water. After that, the wastewater is sent to large tanks (水箱), where the solid waste sinks to the bottom. Then, the solid waste is separated from the water until only tiny bits remain.
The water is then moved to the next treatment area. Here, air is pumped into the water. The air helps bacteria eat the tiny bits of solid waste. Finally, some chemicals are added to kill the harmful bugs you can't see.
The water is clean now and ready to be released and sent back into the water supply. It can be used for everything from watering gardens to filling swimming pools. It's even used to make drinking water! At last, the water has returned to us once again.
A Choose the correct answer. 选择最恰当的答案。
( ) 1. The passage is mainly about ________.
A. why clean water is important
B. how water is used in cleaning
C. how we can stop wasting water
D. the process of cleaning wastewater
( ) 2. Wastewater needs special treatment to ________.
A. make it clean and usable
B. make it have lots of bacteria
C. remove large objects from the water
D. send it to the sewage treatment plant
( ) 3. The ________ helps bacteria eat the tiny bits of solid waste.
A. air
B. bugs
C. wastewater
D. chemicals
( ) 4. What can be inferred about bacteria?
A. They must be kept in water.
B. They are very dangerous in water.
C. They cannot be killed with chemicals.
D. They can sometimes be helpful to us.