I didn’t quite follow him because he explained the theory _____that is too abstract for me.
Sorry, I'm late. I________have turned off the alarm clock and gone back to sleep again.
I posted a book to her three weeks ago. She________have received it.
She________have been to your house. She doesn't know your address.
—I'm sorry, Mrs Smith. I've broken your glasses.—It doesn't matter, Marks, but you________careful.
I can't find the recorder in the room. It________by somebody.