Linkage institutions are structures in a society that connect the government to the people. Interest groups and political parties are both linkage institutions. Interest groups attempts to make the government favour specific policies that would benefit said groups; political parties, instead, try to reach the government by getting their candidates elected.
The unit used to express volume is the cubic meter. This is the SI unit for the volume of a solid, gas or liquid. Volume is also expressed in units like liter, gallon, quart, pint, fluid ounce and cup.