语法：名词性从句Obviously that we do morning exercises every day ___ us good.

C does
that we do morning exercises every day 是一句话作主语，要用单数

B，第一个词是“显然”的意思，后面从that到day是从句，翻译是“显然我们天天做早操对我们有好处”，主语是“做早操”，谓语动词用单数。