A variety of tests is necessary because a range of different activities is more likely to give an accurate overall picture of a student's level than a single assessment.

各种各样的测试是必要的，因为一系列不同的活动比一个单一的评估更有可能给出一个学生水平的准确的总体情况。

A variety of tests would be necessary because a range of different activities would be more likely to give an accurate overall picture of a student's level than a single assessment.

各种测试是必要的，因为一系列不同的活动比单一评估更有可能准确地全面了解学生的水平。