The problem is to determine whether

The problem is to determine whether exposures have occurred before
substantial symptoms are present. This is accomplished through a variety of
medical tests. The results from these tests must be compared to a medical
baseline study, performed before any exposure. Many chemical companies
perform baseline studies on new employees before employment.

結果 (中文) 1:

问题是要确定是否暴露也曾发生过大量的症状是存在的。这被通过各种医学测试。从这些测试结果必须相比医疗在任何暴露前进行基线研究。许多化学公司对新员工就业前进行基线研究。

結果 (中文) 3:

问题是，以确定是否发生之前发生的风险实质性症状是存在的。这是通过各种各样的医学检验。从这些测试的结果必须进行比较的医疗基线研究，在任何暴露前进行。许多化学公司在就业前对新员工进行基线研究。