这句不是强调句.而是宾语从句套主语从句.
因为how many days ago 以及之后的部分是remember的宾语从句.宾语从句应该是陈述句的形式,所以排除C,D
而宾语从句中,a fight broke out between them 是主语从句 ,引导词应该用that,不用when.it 做了a fight broke out between them的形式主语
还原成正常的语序应该是 it was (how many days ago) that a fight broke out between them.