【题目】______ the average age of the population increases, there are more and more old people to care for.
A.Unless
B.Until
C.As
D.While

【答案】C
【解析】句意：随着人口平均年龄的增长，越来越多的老人要照顾。Unless除非；until直到；as因为，正如，随着；while虽然，然而，当……时候。根据语境，故选C。