Which of the following sentences is correct?

only置于句首,强调方式、 条件、 地点、 时间等状语时,主句要进行部分倒装。如果被only所强调的状语为状语从句,该状语从句不倒装,只对主句进行倒装。举个例子：Only in a big city was it possible to buy a new wheelchair。只有在大城市里才能买到新轮椅。// Only when we had studied the data again did we realize that there was a mistake。只有当我们再次研究了这些数据的时候,我们才意识到出了一个错。请注意：如果放于句首的only所修饰的不是状语时,该句不用倒装。例如：Only John can save me。只有约翰能够救我。