Question

i think that's unlikely to happen,but if that___occur,bothAm

Answer 1

这个地方可以有几种方式：1) if that occurs, 2) if that does occur, 3) should that occur, 4) if that should occur.第4种方式是最不常见的,所以不易让人看懂.should就是shall的过去式,是“未来将要发生”的一种委婉表达方式,在表未来时比shall本身意思要弱,所以should在这里就是指“未来可能发生”的意思.