I do not know whether you realize it, but this condition is essential to us.
我不知道你是否了解,但是,这个条件对我们是必要的。
It is possible that there is a definite relation between these paintings and the markings that sometimes accompany them.
有时,这种图画与墙壁上的刻痕共存,它们之间可能有一定的联系。