a. not easy; requiring great physical or mental effort to accomplish or comprehend or endure
a. 困难的
1. Learning a new language can be difficult at first.
学习一门新语言在开始时可能很困难。
2. I find math problems difficult to solve.
我觉得数学题很难解决。
3. It's difficult to make everyone happy all the time.
让每个人一直快乐是很困难的。