Three and three ______ six.
Two threes _____ six.
A. is B. are
Three and three is / are six.
Two threes are six.
为龙老师的解答点赞。我在夸克的《英语语法大全》上找到了相关说明:
请采纳龙老师的解答,上面的截图引文只是作为龙老师解答的一个补充和印证。
赞同龙楠老师的看法,请采纳他的答案。
又如,英国《牛津英语用法指南》第四版的例句(322.21节):
Two and two is / are four. (非正式)
Three fours are twelve. (非正式)