风蚀洼地（aeolian depression）
参考答案：
因风蚀而形成的洼地。洼地的底面如达到地下水面，这里就会成为沙漠中的绿洲。
When he was doing the software development project, he ___________ many problems that he had to solve on his own.
A．came up with
B．came through
C．came across
D．came out
长期保存的价格鉴证档案一般为（）年。
A.10
B.20
C.30
D.50
