—Is Jack on duty today?—It __________ be him. It’s his turn tomorrow.
Keep _______ when I take your photograph.
—How much do I owe you for lunch? —________________. It’s nothing.
It ________ that their plan was practical and successful.
It is considered a good way for students to ________study with pleasure.
It is known to all that a proper amount of exercise ________ to good health.