Being a stay-at-home mom and working is（这里为什么是is而不是are,因为主语有

Being a stay-at-home mom and working是一种状态（既工作又在家当母亲的状态）,因此谓语用is；另外,后一个is的主语也是Being a stay-at-home mom and working.这句话的主干部分是Being a stay-at-home mom and working is something (that从句修饰something) but something (that从句修饰something；once从句做状语).