1. The answer is d. Primary sexual characteristics involve the reproductive organs as a result of sex hormone production (i.e., maturation of the ovaries, breasts, uterus, penis, and testes). Secondary sexual characteristics accompany hormonal changes but are not directly involved in reproduction. They include development of facial, body, and pubic hair; deepening voice; and distribution of fat and muscle.

2. The answer is b. Progesterone causes the uterine lining to mature in preparation for implantation of a fertilized embryo, and it inhibits the production of FSH, which would trigger the beginning of a new cycle. If fertilization does not occur, the increase in progesterone from the corpus luteum also shuts down the production of LH, which sustains the corpus luteum itself. As the corpus luteum begins to disintegrate and progesterone levels fall, FSH production is no longer inhibited and begins anew. Without progesterone, the lining of the uterus cannot be sustained, and it is shed in the form of the menstrual flow. The menstrual cycle then begins again.

3. The answer is d. Boys have higher caloric needs than girls because boys have a greater proportion of lean body mass relative to adipose tissue. A rapidly growing, athletic, 15-year-old boy may need as many as 4000 calories per day just to maintain his weight. By contrast, an inactive 15-year-old girl whose growth is almost completed may need fewer than 2000 calories per day to avoid gaining weight.

4. The answer is b. The best predictor of smoking behavior is having parents who smoke. The influence of friends is greater earlier in adolescence than later during this period. Advertisements—especially those that link smoking with thinness in women—also play a role. Adolescents who are socially skilled are more self-confident and less likely to succumb to the influence of peers to engage in risky behaviors.

5. The answer is b. The timing of puberty can significantly influence how adolescents feel about their new bodies. Girls who develop early and boys who develop late are most unhappy with their bodies, and tend to feel less attractive to the opposite sex. Early-maturing girls are self-conscious about their bodies and subject to teasing from boys, who typically develop later than the average girl. Late-maturing boys appear to be boys among the women and young men in their class, and have more difficulty competing in athletics and socially.

6. The answer is a. Of the many factors that influence adolescents’ choice to become sexually active, the family environment is the most significant. Teens who come from stable families in which parents demonstrate responsible behavior and are open to discussing sex with their children are less likely to engage in premarital sex. Those who do are older at first coitus. Teens whose families are poor, are disorganized, and endorse the view that women are subservient to male dominance tend to become sexually active at an earlier age. Adolescent girls who have goals for their future involving education and career also delay first coitus.

7. The answer is d. Reversibility and ability to speculate about things that seem impossible help to identify formal operational thinking.