单选题 The author regards the new means of water-use reduction under discussion as

(A) wholly effective, but typically ignored
(B) inexpensive, but insufficiently useful
(C) promising, but difficult to implement
(D) necessary, but likely to produce ill side-effects
(E) universally accessible, but unnecessary

A
B
C
D
E

【正确答案】 C

【答案解析】