They forgot to lock the door. ✬

Lock the safe. ✬

I forgot to lock the drawer. ✬

If I lost my key, I wouldn't be able to lock the door. ✬

Lock the door. ✬

The door will lock automatically when you go out. ✬

It was careless of me to forget to lock the door. ✬

Would you please lock the door? ✬

Remember to lock the door. ✬

Please lock the door when you leave. ✬