状语剖析（based on the fact...）附加状语、下加状语、联加状语、外加状语中的哪一种

Tom was ranked the first in his class, based on the fact that he got 98 in the exam, which is higher than anyone elses in his class.

请问这个based on 是什么状语，逻辑主语应该不是主句的主语。四种状语成分里边的哪一种？附加状语、下加状语、联加状语、外加状语？谢谢！

过去分词短语作外加状语，即评注性状语（disjunct)，是说话人对自己句子作的注解、说明。based的逻辑主语为前面整个主句的内容。后面的which从句是修饰98这个分数的非限制性定语从句，是外加状语的内部成分。