选A
在句首的only如果后面跟了副词、介词短语或从句等状语,则主句用倒装结构.如only后跟
的是主语,就不用倒装结构了.例如：
Only when the war was over in 1918 was he able to get back to work．
Only in this way can you learn English well．
Only after a bitter struggle was the aim achieved．
Only the teachers are allowed to use the room．（不倒装）
Only five men were hurt in the accident．（不倒装）