He was hiding the fact that he was an illegitimate child.

He is the main organizer of this event.

He is struggling with his exam studies.

He is struggling with the new project.

In organic chemistry, cyclobutane has a structure in which four carbon atoms are bonded in a ring.

Cyclopropane is a compound often used in organic chemistry.

Cycloalkene is a compound often used in organic chemistry.

Cycloheptane is a compound often used in organic chemistry.

Cycloalkyne plays an important role in organic chemistry.

Cyclononane is a compound often used in organic chemistry.