3. appropriate ，fit，proper，suitable 这一组词均含有 恰当、适宜 之意。
appropriate：非常适合的，具有一种与该人或该事物相匹配的适宜性。常用短语：appropriate to /for。
He always tried his best to give the appropriate examples to illustrate the usage of an expression.他总是尽力举出恰当的例子来说明词语的用法。
fit： 合适的、恰当的，指具有为了达到某项目的、或完成某项任务、或适合于某种用法所需的品质，有时也指人具备所需要的资格或能力。常用短语：be fit fur/to do。
I should say she wasnt fit to do anything of the sort. 我得说她不适合做任何这类事情.
We are here to see that the houses are fit for human habitation.我们来此要使这些房子适合入住。
proper： 合适的、适宜的，指该事物依照某种惯例或情理是无可非议的，或强调通过逻辑思维、推理所确定的事物的适宜性和合理性。常用短语：proper for /to do。
When a child has mastered a difficulty after persistent efforts, praise is a proper reward. 当孩子经过坚持不懈的努力，驾御了一件困难工作时，最合适的报偿是夸奖。
It was proper to say that most Americans belong to the middle class. 说大多数美国人属于中产阶级是正确的。
suitable： 适合的、适宜的、恰当的，用于指人或事物能够与某种场合、环境、要求相适应。常用短语：suitable for。
Theres no denying that his speech is suitable to the oceasion.毋庸置疑他的言辞合时宜。
Do you think this present suitable for the boy of his age?你觉得这份礼物送给他那个年龄的男孩合适吗?