—What are you busy with recently? —We have been looking into how the machine breakdown __________.
Coming into the room, I found them _______ at the table, ________ chess.
Along with the letter was his promise _____he would visit me this coming Christmas.
John opened the door. There _____ he had never seen before.
______, the car stopped all at once.
He ______ busy yesterday, or he ______ you with your experiment.