This lens is used for light concentration.

This lens is used to concentrate light.

He is brushing his lower teeth.

He smiled, showing his lower teeth.

She seemed nervous, biting her lower lip.

She seemed nervous, biting her lower lip.

He was complaining about pain in his armpit.

I plan to spend the afternoon at the library.

The emperor issued an order to the entire army to start the attack.

The emperor ordered the entire army to attack.