改错：These two desks are Lucy andLily`s.

改错：These two desks are Lucy andLily`s.
改错：These two desks are Lucy andLily`s.

改错：These two desks are Lucy andLily`s.
Lucy and Lily`s就是指两个人共有的,而Lucy's and Lily's就是指每人都有一个 ..
可以根据名词的单复数判断 Lucy and Lily`s desk ,而Lucy's and Lily's就接desks.

Lucy's and Lily's.
因为是两张桌子，一人一个

Lucy's and Lily's.

Lucy's

每人一张桌子，要分别表示，
lucy's and lily's

Lucy's