abstraction of relation between variables的用法和样例：
- The relation between variables when the regression equation is linear: e.g.,y = ax + b.
- Study of relation between acute damageand trace elements in serum.
- Measures are being taken to promote the normalization of relation between the two countries.
- Led by researchers at the Massachusetts Institute of Technology, this effort looked at the relations between variables such as total population and the rate of construction of Mayan monuments.