About what percentage of 3- and 4-year-olds in the United States are enrolled in preschool?

Ali is in the hospital about to undergo a brain-imaging process that involves taking many X-rays from different angles aided by the use of a computer. What type of imaging technique is being used?

a) electroencephalography (EEG) b) magnetic resonance imaging (MRI) c) positron-emission tomography (PET) d) computerized axial tomography (CT)

As discussed in the text, hostility is linked to increased risk of coronary heart disease because

a. hostile people are frequently angry, and chronic anger increases the risk of hypertension and coronary heart disease b. hostile people frequently vent their anger and frustration, and yelling or arguing with others increases blood pressure and the stress placed on the circulatory system c. hostile people sometimes bottle their emotions and stifle emotional expressions, thereby causing an increase in heart rate and blood pressure d. hostile people frequently over-exert themselves in an effort to come out on top or to prove that their ideas and efforts are superior to those of others e. hostile people frequently misuse over-the-counter medications and, sometimes, illicit drugs.