His explanation doesn't make sense at all.

His abilities are suited to this job.

He doesn't understand the problem at all.

Honestly, he can't keep a promise.

There is reason in what he is saying.

He gave me a detailed explanation of the problem.

He explained the problem.

No wonder he is so tired, he has been working all day.

No wonder, I understood why he is so tired.

He is my best friend.