He returned the favor because I had helped him before.

He returned the favor because I had helped him before.

I use warm water to make coffee.

He is an expert in acoustics.

Axion is a hypothetical subatomic particle and is considered a candidate for dark matter.

He is my benefactor, he helped me in my difficult times.

His mild personality attracts people quickly.

Where did this sound source come from?

He is playing a new game online.

It's high temperature today, it's hard to go out.