B Why is the Ampere a base unit?

It's easier to measure a current than a charge.

 

This may change, wiki article:

http://en.wikipedia.org/wiki/Proposed_redefinition_of_SI_base_units#Ampere

 

And there are also a number of other reason. One very important property of the base units is that they are technologically/commercially important.. People forget that the SI is mainly a practical system for use in our everyday lives (which is why the Candela is a base unit) ; meaning practical considerations are more important that what is most satisfying from a philosophical point of view.

The re-definition of the SI will see the Ampere (as well as a few other units) be re-defined, but it will still be the base unit for the electrical units,