我来回答：
1.what is her favorite day?的同义句是what day does she like best
2.Helen is favorite subject is biology.的同义句是Helen likes biology best
解析：what is her favorite day意思是她最喜欢哪一天?favorite意为最喜欢的,而like.best与他相同,就用like.best.her的主格是she,就改为用she,问哪一天则用what day
第二句Helen不变,favorite对应like.best,best一般都放在句末,然后Helen是第三人称单数,后面的动词like就要加上s,即likes.
亲,采纳我的吧,我再做任务额.
你也是初一的吧,我也是啊,英语不懂的可以问我哦