答案：A

题目分析：考查定语从句和强调句：句意：就是我们要去参观的农场每年为附近的城镇提供很多绿色的蔬菜。第一空填引导定语从句，先行词是the farm，定语从句中pay a visit后面缺少介词to，用介词to+which，第二空是that，这是强调句型，强调的是the farm to which we are going to pay a visit，也就是这句话的主语，去掉强调结构，这句话是the farm to which we are going to pay a visit provides large quantities of green vegetables for the nearby town every year.选A。