She read the letter which upset me. vs She read the letter, which upset me.

Hi everyone :slight_smile:
Please I was woundering if someone could help me with this question my son has set me

Explain the difference between the following pairs of
sentences. Are there any pronunciation differences?

She read the letter which upset me.
She read the letter, which upset me.

He keeps his canary in the bathroom.
He keeps his canary in the bathroom?

They went to Austria and Italy.
They went to Austria and Italy …