I suppose she is not serious, ___?

I suppose she is not serious, ___?
A、do I
B、don't I
C、isn't she
D、is she
【正确答案】：C
【题目解析】：若主句为I （we） think（believe, suppose, consider）＋that从句时，问句部分的助动词和主语与that从句内的动词和主语保持一致。若主句为I （we）don't think（believe, suppose, consider）＋that从句时，从句为否定意义，问句部分的助动词和主语仍与that从句保持一致,用肯定形式。​若主句为非第一人称主语＋think (believe, suppose, consider)+that从句时，问句部分的助动词和主语与陈述部分的助动词和主语保持一致。