difficulty是名词，没有比较级，一般比较级是指形容词或副词才有比较急。
那么difficulty名次的形容词变体是difficult，difficult的比较级是more difficult表示更难的，例如：
1、While the top of the ocean is well studied， its depths are more difficult to explore.虽然海洋表面已得到了充分的研究，但深海更难探索。
2、Exercise energizes you， so it is more difficult to relax and have a peaceful sleep when you are very excited ．运动使你精力充沛，所以当你非常兴奋的时候会更难放松和进入睡眠。
