You are going out for the evening with your friends, who are parents of a ten-month-old girl. The babysitter is new, and the baby is asleep when she arrives, so the parents decide not to wake the baby to say goodbye. Lately, the baby has been increasingly grumpy about being left at home, and, they reason, there's no point in causing a scene unnecessarily. The movie is great, but when you return at 11:00, the sitter tells your friends the baby awoke two hours earlier, screamed hysterically for 45 minutes without letting herself be comforted, finally falling asleep. The sitter is exhausted, too. From what you have learned about infants, why do you think the baby was crying, and what can her parents do to prevent such a situation from occurring again?