请教一个OG的问题

7. Dr. Hakuta's research among Hispanic children in the United States indicates that the more the children use both Spanish and English, their intellectual advantage is greater in skills underlying reading ability and nonverbal logic.

(A)  their intellectual advantage is greater in skills
    underlying reading ability and nonverbal logic

(B)  their intellectual advantage is the greater in skills underlaying reading ability and nonverbal logic

(C)  the greater their intellectual advantage in skills underlying reading ability and nonverbal logic

(D)  in skills that underlay reading ability and nonver­bal logic, their intellectual advantage is the
    greater

(E)   in skills underlying reading ability and nonverbal
    logic, the greater intellectual advantage is
    theirs

这道题的答案是C，但我觉得C中间似乎缺少一个谓语动词。不知道我理解的是否正确？