The caption of the article reads "<em>Water </em><em>Flowing from </em><em>Toilet to Tap</em><em> may be Hard to Swallow".</em>
In the fourth sentence the writer states:
<em>And therein lies a </em><em>marketing challenge</em><em> that can even be greater than the technological one.</em>
The Marketing challenge here refers to the fact that it would pose a challenge to the government of California to convince its citizens on how to accept that drinking recycled water is safe.
Conclusievly, the correct option is C.
See the link below for more on the subject of recycled water in California:
brainly.com/question/11191322
