Most middle-class families' attitude towards water conservation is due to their ____________.
The most appropriate answer to complete the sentence is Option D.
In the latter part of the passage, Surti describes the attitude of the middle-class families towards issues like these. The passage refers to a term of ‘sheer indifference’ in the sixth line of the second paragraph highlighting the attitude of the middle class. Eventually the water problem is gross and the reason for it is lack of concern, as mentioned in Option D.
The other options A, B and C, refer to lack of knowledge, money and expertise, which is neither a problem nor a matter of concern for the middle class, hence are not the correct answers.