这组词都有“加强”的意思，其区别是：
increase: v.指数量上的增加。
➤ The number of people has been increased.
人数增加了。
reinforce: v.增援，一般用于军队或警察的行动；(以添加材料等)加固。
➤ A police officer saw three thieves robbing a bank and radioed to reinforce him.
一位警察看到三个盗贼抢劫银行，用无线电话要求增援。
intensify: v.使变得更强烈、剧烈，加剧，相当于to become more intense or intensive。
➤ intensify colors
加深色彩intensify hatred加深仇恨
strengthen: v.加强，巩固，增强，相当于to become stronger。
➤ Exercising every day strengthens the heart.
每天锻炼可以提高心脏的功能。
➤ Competition, they believe, strengthens the national character rather than corrupt it.
人们认为竞争加强了民族性而不是破坏了它。
aggravate: v.加重(负担、罪行、病情等)，使之恶化。
➤ I hurt my foot, then aggravated it by trying to walk too soon.
我的脚受伤了，而过早的下地走路又加重了伤情。
enlarge: v.扩大，多指具体物品如相片的放大。
➤ enlarge photograph
放大照片enlarge a house扩建房屋
stretch: v. (有弹性地)伸展，延伸，并有可能超过限度；伸长、伸出(身体某部位)并绷紧肌肉(尤指在放松后或为了够着某物)。
➤ The pullover stretched after I had worn it a few times.
这件套头毛衣我穿了几次之后就撑大了。
➤ Having finished their morning work, the clerks stood up behind their desks, stretching themselves.
完成了早间工作之后，职员们站到桌子后面伸伸懒腰。
expand: v.指范围、体积的扩大、增大，也可以指内容或细节的充实。
➤ The balloon expanded, then exploded.
气球先是膨胀，然后就爆破了。
reinforce: v.增援，加固。
magnify: v.放大，指用透镜或显微镜使物体看上去大一些。
➤ His eyeglasses magnify words so he can read them.
他借助眼睛把字放大以便能够阅读。
amplify: v.扩大，增加，尤其指通过增强电压或电流使声音扩大；补充叙述(故事、事件等)。
➤ We must ask you to amplify your statement.
我们得请你对你的说法作进一步的说明。