1 回答
to which若しくはthat to which全部は無視していいと思います。
→The question is what is the economic or attainable yield, that the best farmers would aspire under the current economics?
か→The question is what is the economic or attainable yield, the best farmers would aspire under the current economics?
that to which の役割として、とくにありません。頭よくきこえるため、変に複雑な文章にする役割くらいでしょうか。