A primary source is when someone founds a real ancient thing that someone wrote or draw a long time ago
You have to connect the other terminal of the primary someplace, be it ground, or be it one of the other hot phases. Convention has it being ground. (I assume you are talking about a distribution...
Because all colors are made by mixing primary colors together. Different ratios of primary colors make all the different colors.
because wit hthose colors you can make the other colors.primary = first;basic.