1. Because water is polar, it can break down both solids and gases. （Reading）
What we eat is broken down in the stomach.
Firemen had to break the door down to reach the people trapped inside.
The old house broke down in the heavy rain.
The talks between the two sides broke down.
The car broke down after half an hour’s drive.
His health broke down under the pressure of work.
Hearing the news, she broke down and cried.
2. Marine animals and plants take advantage of the density of water.（Reading）
take advantage of sth./sb. 表示“充分利用；（为达到个人目的而不正当地或不老实地）利用某人或某物”。如：
You should take advantage of the fine weather to paint the fence.
He took advantage of the housing shortage by renting out his basement.
Don’t take advantage of others’ weaknesses.
Two beggars took advantage of the little boy and cheated him out of $3.
3. Most animals and plants are sensitive to large or sudden changes in temperature, so the ocean is a safe and comfortable habitat.（Reading）
be sensitive to表示“对……敏感/易生气/反应过激”。如：
His ears are highly sensitive to any unusual sound in the machine.
A writer mustn’t be too sensitive to criticism.
This creature’s natural habitat is the jungle.
4. An estuary is the body of water where a river meets the ocean.
There the brook meets the river. 在那里小溪汇入河流。
The village is located where the two rivers meet.
5. Estuaries also contribute to the economy through tourism and fishing. （Integrating skills）
Everyone should contribute what he or she can afford.
Many countries contributed aid for refugees in Africa.
She has contributed several poems to literary magazines.
The famous professor’s lecture has contributed greatly to our understanding of the difficult subject.
Does smoking contribute to lung cancer?