彼は一生懸命英語を勉強したに違いない。の英語

He must have studied English hard.

He is very zealous in his study of English.

He is getting on very well with his English.

He had long since given up studying English.

He says that he will study English harder.

He applied himself closely to the study of English.

He went to America to study English.

He went to the United States to study English.

He's working at his English.

He went to America to study English.

He went to the United States to study English.

It was difficult to understand his English.

She studied English as hard as she could.

He mastered English easily.

He is busy learning English.

He never speaks English without making mistakes.

He went up to Tokyo with the intention of studying English.

It seems he got some confidence in his English.

He went there to learn English.

His English improved in no time.

He is studying English.

He developed his English skill while he was in America.

He improved at English suddenly.

He has made rapid progress in English.

He had never studied English before he went to the United States.

He has a good grasp of English.

I have become able to understand his English well.

He speaks English very well.

His English is quite good.

He has made a full study of English―made an accurate study of English.