Learning Modern English is important for smooth international communication.

He is interested in the study of constructed languages.

Nuclear fission is a powerful phenomenon that generates energy.

He remained silent and didn't say anything.

He was promoted to Admiral of the Fleet.

I am planning to go to Copenhagen next week.

He is an expert in sociolinguistics.

I am very interested in sociolinguistics.

He is an expert in nuclear physics.

He has already finished writing the report, so we use the present perfect form.