I play basketball with my friends every weekend.

The stock price plummeted.

The stock prices plummeted, causing investors to panic.

It's difficult to calculate the sum of this series.

The lifeboat was floating in the sea.

He is my enemy.

When we got lost in the mountains, the rescue team helped us.

The police began their investigation into his crime.

The police are investigating the incident.

He is always dedicated to the pursuit of knowledge.