能一起用，例如：
1、If you smoke then the whole respiratory system is constantly under attack.如果抽烟，整个呼吸系统就会一直受到损害。
2、If his experiences then had been carefully recorded， it would undoubtedly have made a suspenseful and moving book.若是把他所经历的事实记录下来，那就是一部充满着大智大勇，惊心动魄的小说。
3、If he is guilty then， by inference， so is his wife.如果他有罪，那么由此可以推断他的妻子也同样有罪。