Scientists have many theories about how the universe into being.
He hurried to the booking office only ________ that all the tickets has been sold out.
—Can those ________ at the back of the classroom hear me?—No problem.
Reading is an experience quite different from watching TV; there are pictures ________ in your mind instead of before your eyes.
—The last one ________ pays the meal.—Agreed!
If water becomes increasingly scarce in decades ________,water shortage will become a hot issue all over the world.