His stubbornness sometimes causes problems.

He launched a project to provide educational opportunities for children in developing countries.

This story is very strange, it's hard to understand.

He shook his head up and down.

He picked up the vajra staff and began to pray quietly.

She took a facesitting pose.

She has mastered the technique of facesitting.

Because of his color blindness, he has difficulty distinguishing between red and green.

The trolleybus is very convenient as a means of urban transportation.

The cricothyroid muscle is an important muscle for adjusting the tension of the vocal cords.