随着社会经济的发展，消费者消费心理也会不断变化，体现了消费者需求的（）特征。
参考答案：发展性
When they heard the ___________ news，they got very ___________．
A．frustrating, frustrated
B．frustrated, frustrated
C．frustrated, frustrating
D．frustrating, frustrating
选用治疗急性坏死性溃疡性牙龈炎最敏感的抑菌药物是（）
A.四环素
B.金霉素
C.磺胺类
D.甲硝唑
E.青霉素
