She is very avtive, ____ her age.

选择D,因为considering 可用作介词,作“鉴于”、“就……而论”解.
She is active , considering her age.意思是就她的年龄而言,他（算是比较）活跃的了.

d is correct.Look at the following example again,you will understand its meaning and usage:
We get to see her breasts on two separate occasions fairly early in the
movie. Not a bad body, especially considering her age at the time, but the scenes
were brief and they pale sharply in comparison to Olivia's nudity.

支持一楼的答案!

d.considering

选D.considering 的意思是考虑到...,considering 在这里是非谓语形式,其实也可以看是一种固定的表达法啦,就像gernerally speaking,judging by/from ,我们都不去深究为什么是用speaking ,judging ,而不是用judged.
eg.Generally speaking , his work is of a high sta...

c 作为
作为她的年龄她活泼
翻译的有点怪

D,

答案是D，整句的意思是：考虑到她的年龄，她很活跃。
considering在这里是非谓语形式，表示补充说明。