not until 的倒装求解

题目

not until 的倒装求解

-------When shall we go planting trees in the hill?
  -------_______it begins to rain , they don't need watering .
A.Not until    B.Since    C.Till     D.Unless

我书上的答案是B,但网上的答案是A,我想问一下Not until放在句首,后面的句子不应该用倒装吗?

答案

正确答案是A.我感觉they前面应该加一个连词,就不会产生歧义了.因为这是问答,补全问答结构就是.------When shall we go planting trees in the hill?------We shall not go planting trees in the hill until it begi...