PAST PERFECT or PAST SIMPLE
After they _______ (enter) the restaurant they were served.
After they had entered the restaurant they were served.
I didn't use my credit card because I ______ (lose) it
I didn't use my credit card because I had lost it
They didn't tell me that Easyjet _______ (cancel) the flight.
They didn't tell me that Easyjet had cancelled the flight.