The evidence that is most relevant to the claim is "Students' reading skills increased by two grade levels when they
learned a second language."
Considering the claim is about the positive impact of learning a second language on reading skills, the best piece of evidence is "Students' reading skills increased by two grade levels..." because this evidence proves the claim, is based on facts (statistics) and the author can be trusted.
Learn more about claims in: https://brainly.com/question/14551819
#SPJ1