I buy gifts for my mum.(改为一般过去式)
I____gifts for my mum last week.
①核膜的有无
②核糖体的有无
③细胞壁的有无
④膜上磷脂的有无
“胡人有妇解汉音,汉女亦解调胡琴”,这首诗写于元末,反映了元朝( )