Talk about C.

C is the unit coulomb of charge (also the symbol of capacitance)

E is the electric quantity of electron, and it is the electric quantity of meta-charge. The charge of all charged particles is an integer multiple of that of elementary charge.

I is the symbol of current, indicating the amount of electricity flowing through the conductor per unit time (I=q/t).

A is the unit ampere of current.

As for contact. The relationship between physical quantities is a formula. The relationship between physical quantities and units is only my own experience. For example, the symbol of length is L or H, and the unit is meter (m). This is the same reason that C is the unit of charge and A is the unit of current.