It's difficult to understand his explanation.

He increased the time spent together to deepen his relationship with her.

They are my best friends.

He goes to the gym frequently.

He goes to the gym frequently.

It's difficult to understand his explanation.

The door opens.

When he opened the window, fresh air flowed into the room.

When he opened the window, fresh air flowed into the room.

We discussed to deepen our mutual understanding.