2,Tom is____brother.A,Lucy and Lily's B,Lucy's and Lily C,Lucy's and Lily's D,Lucy and Lily.请解释

2,Tom is____brother.A,Lucy and Lily's B,Lucy's and Lily C,Lucy's and Lily's D,Lucy and Lily.请解释
2,Tom is____brother.A,Lucy and Lily's B,Lucy's and Lily C,Lucy's and Lily's D,Lucy and Lily.请解释

2,Tom is____brother.A,Lucy and Lily's B,Lucy's and Lily C,Lucy's and Lily's D,Lucy and Lily.请解释
选a 后一个人名加`s 前一个不加