OG-107

107. Downzoning, zoning that typically results in the reduction of housing density, allows for more open space in areas where little water or services exist.
(A) little water or services exist
(B) little water or services exists
(C) few services and little water exists
(D) there is little water or services available
(E) there are few services and little available water
OG又这样一段解释：
Also, since water and services are being discussed as a pair, they should logically be treated as a compound subject requiring a plural verb; thus, the singular verbs exists (in B and C) and is (in D) are wrong.

不明白为什么D中的is是错误的...请教