有关老年心理变化的主要观点有（ ）。
A．老年丧失期观
B．毕生发展观
C．认知发展观
D．道德发展观
参考答案：A,B
With some technical problems to be solved, it may be a while _____ the system is put into use. [ ]
A. when
B. after
C. since
D. before
简述梭伦改革的重要内容。
