[单项选择]咖啡因，茶碱等黄嘌呤生物碱的特征反应
A. 双缩脲反应
B. 紫脲酸铵反应
C. 与香草醛等缩合显色
D. 钼硫酸显色反应
E. 硝化显色反应

Have you ever been afraid to talk back when you were treated {{U}} (47) {{/U}} Have you ever bought something just because the salesman talked you into it Are you afraid to ask someone for a date
Many people are afraid to assert (表现) themselves. Dr. Alberti thinks it’s because their self-respect is low. "Our whole {{U}} (48) {{/U}} is designed to make people distrust themselves," says Alberti. "There’s always {{U}} (49) {{/U}} around--a parent, a teacher, a boss--who ’knows better’. These superiors often gain when they chip (削弱) away at your self-image."
But Alberti and other scientists are doing something to help people. {{U}} (50) {{/U}} themselves. They {{U}} (51) {{/U}} "assertiveness training" courses--AT for short. In the AT courses people learn that they have a right to be themselves. They learn to speak out and feel good about doing so. They learn to be more {{U}} (52) {{/U}} without hurting other people.
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