【在线等答案】如何理解这个完型的选择?

【在线等答案】如何理解这个完型的选择?
At its most basic, a job is just a collection of tasks and duties. An employee’s enjoyment of his or her job will thus largely depend upon whether or not he or she is happy with the particular mix of tasks and duties allocated to that position. Naturally, each and every member of staff is different—some employees want to do easy, routine tasks without any responsibilities at all, whilst others prefer challenging, varied ones and are pleased to accept any additional responsibilities offered to them. Of course, with a job there are more【 factors】 in play than this: work conditions, pay, working relations and future prospects are relevant too. Nevertheless, tasks and duties are the central feature, and should therefore be considered as a separate issue in themselves
【】里头的是正确答案,其他的选项有： pieces ； roles ； parts 我一直不能理解为什么选factors,能讲讲吗?那句话的含义我也不太明白,不知道in paly than在这里起什么作用?