1. Let's take a break
= Let's have a rest.
2. I know it from A to Z.
= I know everything about it.
3. The waste water pollutes the river.
= The river is polluted by the waste water.
= The waste water brings pollution to the river.
4. We must reduce the use of plastic bag.
= We must use fewer plastic bags.
5. The Reads are having lunch now.
= The Read family are having lunch right now/at the moment.
6. We all wonder why he is so unhappy.
= All of us want to know the reason for his being unhapppy.
7.My sister put on weight again
= My sister gained weight again.
8.I will keep it in mind.
= I will remember it.
= I won't forget it.
参考资料:英语牛人团