1. One day，he came up with an idea he would pluck up all of his crop a few inches.
解析考查同位语从句的引导词。因后面是一个完整的句子，且该句是说明空格前面an idea的具体内容，所以是同位语从句。从句结构完整，故要用that引导。
答案that
2. is important is that we let others know we care about them.
解析考查主语从句的引导词。根据句子结构可知，系动词is前的句子缺少主语，表示“重要的事情”要用what。
答案What
