She was hiding the sadness concealed within her smile.

The quality of this product is very high.

He will succeed sooner or later.

This festival is held every year.

He spends a lot of time studying.

He reads a lot of books.

It's difficult to solve a part of this problem.

This bottle contains an unknown liquid.

This enzyme helps with chemical reactions in the body.

Microglia are immune cells in the brain, playing a role in maintaining the health of the nervous system.