In chemistry, we use projections to represent the shape of molecules.

It's difficult to solve this monomial expression.

He admitted that it is difficult to execute the plan, saying 'it is easier said than done.'

Well then, I'm off.

He is undergoing training for extravehicular activity.

He engaged in an extravehicular activity from the spaceship.

We crossed the sea by catamaran.

The shipworm is known for eating wood.

Alicyclic compounds play an important role in organic chemistry.

He was interested in the ancient boustrophedon style of writing.