difficult比较级为more difficult
例句
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。
3.
Some people find this more difficult than others.
这件事有人觉得难，有人觉得不难。
