Dina,for months trying—to find a job as a waitress,finally took a position at a local advertising agency.
蒂娜,数月来试图找一份服务员的工作,最终在当地一家广告公司就职.
选A,中间部分：___for months to find a job as a waitress应该是个定语结构,修饰主语Dina的,如果把这部分换成个定语从句就是：Dina who had struggled to moths to find a job as a waitress.
把定语从句换成非谓语动词形式,去连词,去主语,谓语动词是主动式,改成了struggling.选择A比较合适.以上是我个人的看法.
可能你会问B为什么不选,它的完成式正好表示动作发生在谓语动词之前,但是,有一条我不是记得很清楚,分词的完成式应该是不可以用来充当后置定语的.