Lucy and Lily ______ sister.They study in the same school.(2009北京市)答案是are,为什么这里sister不加s?

Lily was born in 1990.So was Lucy.Lily and Lucy ______ _______ in ______ _______year. my seat is between ______ in the classroomA lucy and lily B lucy's and lily C lucy and lily's D lucy's and lily Lucy and Lily look the same改为同义句是：Lucy and Lily is have______ _______ ______.以上怎么填? ( ) 1.Mrs Green is ______ mother.They are ______.A Lucy and Lily’s; twins B Lucy’s and Lily’( ) 1.Mrs Green is ______ mother.They are ______.A Lucy and Lily’s; twins B Lucy’s and Lily’s; twins’C Lucy and Lily’s; twin D Lucy’s and Li Maria sits ------ Lucy and Lily. Lucy and Lily are twins.同义句转换：Lucy ----- ----- ----- ----- Lily. 选择 Is the woman your Chinese teacher No,She's ______ English teacherA.Lily and LucyB.Lily and lucy's C.Lily's and lucyD.Lily's and lucy's 's 的用法 什么共有 Why There are some similarities ______ Lucy and Lily.（用适当的介词填空） ______ Lucy and Lily go home at seven?A.Do B.Does C.Is D.Are 露茜和莉莉在某些方面看起来一样.用英语怎么说______ ______ ______,Lucy and Lily look the same. They aren'______ (I) books. They're ______ (Lily and Lucy).用所给单词的适当形式填空. she is lucy and she is lily where are还是is lucy and lily These are( )friends A.Lucy's and Lily's B.Lucy and Lily C.Lucy and Lily's D.Lucy's and Lily 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 This room is ___ .A.Lucy and Lily B.Lucy's and Lily C.Lucy's and Lily's D.Lucy and Lily's 语法说明 lucy and lily b(?) have blond hair. lucy and lily ----------(not like)apples