A pellet of. pure U-235 the size of a small marble has enough energy in it to drive a modern automobile 100,000 miles or four times around the earth. But no scientists have yet discovered any way of getting any power from just one ounce of uranium. A single ounce of silvery-white U-235 has locked up in it the heat of 30,000 gallons of gasoline. Unfortunately, the motor for generating atomic power, unlike a gasoline engine which can run with only a cupful of gasoline in the tank, requires a full charge of uranium before it will operate at all. The atomic engine has the drawback that it will not operate unless its "gas tank" is full to the brim. Furthermore, the atomic engine must have a full supply of its uranium or it will not continue to operate once started.

Q. Underline a phrase which shows that the automobile is a flexible user of fuel.