Concept:The site for a fish-pond should be chosen based on natural conditions that directly affect pond construction, water holding and supply.
Explanation:Topography, soil type, and water availability are critical physical factors for a good fish-pond site.
A suitable slope and land shape help in easy drainage and water control.
The right soil type, such as clay, reduces water loss through seepage.
A reliable water source is essential to maintain the pond level.
In contrast, manure is not required to be present at the site from the beginning.
Manure can be bought or brought in from another place when needed.
It is a management input rather than a site selection factor.
Therefore, among the listed options, manure availability is the least important.
Answer:D. availability of manure