We plan to sail on a yacht during the summer vacation.

Studying the history of the Imperial Examination is important for understanding the past of our country.

Maintaining oral hygiene is very important for overall health.

He is working at the pithead.

Sexual intercourse is one of the basic human desires.

They were having sex in secret.

This beautiful zoisite necklace is my favorite.

This fossil is made of carbon.

We conducted a meta-analysis on this issue.

This ring is made of lazurite.