The kind of thoughts that keep a person from falling asleep can arise in either half of the brain. Ttherefore, a person being prevented from sleeping solely by such thoughts would be able to fall asleep by closing the eyes and counting sheep, because this activity fully occupies the left half of the brain with counting and the right half of the brain with imagining sheep, thereby excluding the sleep-preventing thoughts. According to the hypothesis, for a person to use counting imaginary sheep as an effective method of inducing sleep, which one of the following must be true? ['The person is able to imagine a wide variety of things.', "Thoughts of sheep rarely, if ever, arise in the person's dreams.", 'Thoughts of sheep would not keep the person awake at that time.', 'Thoughts of sheep would induce sleep in the person whenever those thoughts arose.']