The apple or an apple?

Did you remember to lock (a)   kitchen door before we left?

I shouldn't drink (a)   coffee. It keeps me awake at night.

Jane is allergic to (a)   cats. She starts sneezing when one comes near her.

Can you turn on (a)   air conditioning? It's boiling in here!

José and Charlotte are going away (a)   next weekend.

Are these (a)   keys you were looking for?

I wasn't feeling very well yesterday, so I didn't go to (a)   work.

(a)   river which runs through Paris is called the Seine.

What (a)   beautiful day! I love it here.

It looks like it's going to rain. Take (a)   umbrella!