This problem is very difficult.

I walk in the park every day.

I walk to school every day.

The swelling in his leg is so severe that it's hard for him to walk.

I was watching the balloon swell.

I thought his behavior was really cruel.

Aldehyde is a very important compound in organic chemistry.

I think his behavior is unjust.

I think his actions are completely inhumane.

It seems like he has been poisoned by something.