Nonrestrictive clauses are those which are set off by commas from the rest of the sentence. I'd choose the answer <u>which<em /></u> as the correct one, because yet introduces independent sentences, and that and while introduce restrictive clauses. For example: The price, which was very high for me, was quite reasonable for Frank.<u />
One year after Du Bois’s death, the Civil Rights Act of 1964 passed in the United States; it included many of the reforms that Du Bois had fought for during his nearly 100-year lifetime.
