Response b, "Voting by mail became the main way to vote in many state elections because of the coronavirus," is also a valid statement based on the passage. It supports the idea that states shifted to mail-in voting in response to the pandemic.
However, the evidence provided specifically mentions states conducting their primary elections almost entirely by mail, which serves more directly to illustrate the challenges faced by Native Americans with nontraditional addresses.
While both responses (b and d) are relevant to the context of the passage, response d is more directly supported by the statement provided, as it ties directly to the challenges faced by indigenous voters when voting by mail due to their nontraditional addresses. Thus, while b is a correct observation regarding the context of voting by mail, d is the best answer specifically related to the evidence given.