高手请指导：______ of cause and effect中填law还是relation?

高手请指导：______ of cause and effect中填law还是relation?
这是完形填空上的一句话,填law还是填relation呢?
原文：
Another step to problem-solving is to help children see the _____ of cause and effect.If a child knocks over a glass,it will fall and break,He or she might like to write on the wall.But the pencil always leaves a mark.Soon the child will see the links between cause and effect,and then he or she is on the road to growth.Seeing someone else knoce over a galss,he or she now knows that it will break.