It reported a net loss of $ 5.6 billion for fiscal 2016, the 10th straight year its expenses have exceeded revenue.Meanwhile, it has more than $120billion in unfunded liabilities, mostly for employee health and retirement costs. (这理的it代指的是USPS是美国邮政管理局)

1 请问这里的the 10th straight year its expenses have exceeded revenue作什么成分？ 

2 mostly for employee health and retirement costs.这一部分是介词短语作非限制性定语还是mostly副词起强调作用？ 求老师解答!