彼は勉強中であった。の英語

I found him at his books.

He applied himself to his study.

He is doing his work.

He's now studying.

He's studying.

He's studying now.

He concentrated on his studies.

He studied very hard.

He studied on his own.

He studied on his own account.

He has risen by dint of perseverance―（他動詞構文にすれば）―Simple perseverance has raised him in the world.

He is diligent in his studies.

He is hard at work―busy at work―busy working―working away.

He is working in earnest―in real earnest―in sober earnest―in sad earnest.

He is always studying.

He started to study in (good) earnest.

He started to study in earnest.

He's coming along nicely with his studies.

He is intent on his studies.

He didn't study at all.

He is, indeed, a hard worker.

He began to study in earnest.

He neglects his studies

He is neglectful of his books.

He was at his books all day.

He is diligent in his study.

He is at his desk.

He is studying at his desk.

He studied like one possessed.

He is lazy in his study.