1、困难：difficulty；difficult；hard；trouble；bump；rub。

2、例句：I now know that its not always easy to see what should be done and even harder actually to do it.现在我知道，认识到什么是应该做的并不容易，而真正去做就更加困难了。

3、Some users may be unable to see, move a mouse, or may face any number of challenges when using a computer.在使用电脑时，有些用户也许无法看见或无法移动鼠标，或者会面临很多其他困难。