问题补充：
---Is mother a teacher? ---Yes, and Lucy and Lily are.
A. Lucy and Lily’s, twin sisters
B. Lucy and Lily’s, twin sister
C. Lucy’s and Lily’s, twin sisters
D. Lucy’s and Lily’s, twin sister
答案：
(答案→)A. Lucy and Lily’s, twin sisters
B. Lucy and Lily’s, twin sister
C. Lucy’s and Lily’s, twin sisters
D. Lucy’s and Lily’s, twin sister
解析：在表示两个人共有某个东西时，’s要加在最后的那个人后面，Lucy and Lily 是复数，故选A
