Groundwater pollution has become a serious environmental problem.

I saw various aquatic creatures at the aquarium.

The proverb 'If you want to shoot the general, first shoot his horse' means that to achieve a big goal, you should start with small steps.

He crossed many mountains and rivers to meet her.

Please remember this old proverb, 'The friendship of a gentleman is insipid as water.'

He said, 'Man shall not live by bread alone,' teaching me that spiritual satisfaction is also important.