Question

3. The reason          his plan was that it was not practical and could not be carried out at all. (turn)

我拒绝他的计划的原因是那个计划一点也不实际，而且根本无法实施。

Answer 1

3. why I turned down考查why引导的定语从句的用法、,关系副词why引导的定语从句用于reason 后，等于for which „ turn down表示"调小，拒绝"_c, 此外关系副词还有：when, where, how等。