center 指三维空间的中心点，也可比喻抽象事物的中心。
middle 一般指时间、空间或过程两端间等距的部分。
heart 指事物最内部或最重要的部分，表地理位置时可与center换用。
core 指某事物固定的中心部分或最重要的核心部分。比喻意义指某物的精华。
midst 书面语用词，指在一个群体的深处或在某活动的进程中。
参考例句
1. John sits in the middle chair, between Ann and Louis. 约翰坐在安和路易斯中间的那张椅子上。
2. At last: Fill the data investigating whether in form middle. 最后：填写调查的数据无论是在形式中东。
3. Asia, North America, South America, Oceania, Middle East, Europe, Africa. 亚洲，北美洲，南美洲，大洋洲，中东，欧洲，非洲。
英英解释
n.
1. an area that is approximately central within some larger region
2. an intermediate part or section
3. the middle area of the human torso (usually in front)
4. time between the beginning and the end of a temporal period v.
1. put in the middle
2. being neither at the beginning nor at the end in a series
3. equally distant from the extremes
4. of a stage in the development of a language or literature between earlier and later stages
5. between an earlier and a later period of time
