The general public has very little idea of what agriculture is about.这里为什么用of what?

题目

The general public has very little idea of what agriculture is about.这里为什么用of what?

答案

have very little idea of...对某方面知之甚少.
只有what才能做双重成分,即介词of的宾语和介词about的宾语（换成正常语序about what agriculture is就能看出来了） .
所以用of what.