I have a severe headache and can't concentrate on my work.

He is studying hard, concentrating for the exam.

He is concentrating on studying for the exam.

I think his behavior is unjust.

I think his actions are completely inhumane.

Aldehyde is a very important compound in organic chemistry.

He was poisoned after eating something.

It seems like he has been poisoned by something.

I thought his behavior was really cruel.

He is looking for a new job.