Count unique licence plates per refuelling

[bintoito]

Hi guys,

i need a formula that counts the unique license plates - repeated dozens of times, each per refuelling throughout the year - but also that takes into account the fact that each license plate belongs to a determined segment

For ex.
column A lists various license plates, one per each refuelling value (in column B) and on column C we already have that the license plate from column A belongs to the car segment X.
The objective is for me to count that segment A has 2 cars, segment F one, etc....

just to clarify: I need to count each license plate irregardless of it being 12-AB-34; the xls I'm looking at has over 40,000 lines so the main point is just to know the number of unique license plates that exist in that particular segment

example xls attached (or so I hope)