only when可以不是引导从句吗？ onlywhen
地点状语放句首倒装 完成时怎么倒
你指的前倒和后倒是什么意思？
相关语法规定如下：
如果only引导状语（或状语从句）放在句首时，句子（或主句）必须采用部分倒装语法，即把 句子（或主句）的 be动词/助动词/情态动词放到主语之前。
如果only引导的是状语从句，从句句序不变，主句部分倒装。
如果only引导的不是状语，则句子无须倒装。
如：
Only in this way can you solve this problem.
Only when it rains does he go to school by bus.
倒装高手请进Only when he had done it___that he had made a mistake.
选C，only修饰副词，介词短语，状语从句置于句首，句子要部分倒装，尤其是在修饰状语从句时，状语从句不倒装，主句部分倒装，将助动词置于主语之前。因为he had done 在realize 动作之前发生，所以realize用过去是就行了
only引导倒装句时的用法.
only 的用法
.only位于句首修饰壮语要倒装
只有倒那时我才将会有机会实现我的梦想.
will 是谓语的一部分因倒装提前了.再如
only in this way can you learn english well
是only引起的倒装句,will 是助动词,如果这个句子正过来说就是 I will have a chance of
achieving my dream only then
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）
注意，only和所修饰的状语如果不在句首，则不倒装。
如：
The boy was helped out only when his father arrived in a hurry．
Only then did he realize the importance of English
只有在那时候他才意识到英语的重要性。
only then ,是过一小会儿的意思，一般用在句首，引导倒装句。
例句Only then did he realize the importance of English．
解析：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。
再比如
Only when the war was over in 1918 was he able to get back to work．(倒装句）
Only five men were hurt in the accident．（不倒装）