15. I wonder if it was ______ what I had said ______ she ignored me.
A. because, 不填 B. because of, that C. because of, so D. because, why
16. Without facts, we can’t form a worthwhile opinion, for we need to have factual knowledge ____ our thinking.
A. which we base B. upon which we base C. which is based D. upon which is based
