细节1, in part because the viruses themselves follow an infectious cycle in which, if protected from direct sunlight, they may remain virulent for many years
细节1,but population ecologists had usually considered viral disease to have contributed to the decline once it was underway rather than to have initiated it
主旨,提出1个观点:临时工多是因为first time和reentering people---反驳---提出2个原因---提供解决方案