I agree with everything vlade5394 posted, but add "D" to the "A" or "B" shop too.[/quBote]
"D"shops can be added, but a complete understanding requires yet more details. There are also, "D," "E," and "F" shops. They are performed identically to "A," "B," and "C" shops respectively. The difference is how they are assigned. They are randomly assigned in addition to the regularly scheduled shops. Because shoppers might care more about how to do them rather than how they are assigned, I prefer to think there are only three types of shops.
Happily shopping Rhode Island and nearby Massachusetts and Connecticut