How many unique numbers do we use in base 5

-- In base-10 (decimal), there are 10 unique symbols ... the digits from 0 to 9.

-- In base-2 (binary), there are 2 unique symbols ... 0 and 1.

-- In base-5, you need 5 unique symbols.  You could use the digits 0 to 4,
or you could use other symbols, like %, #, @, +, and Δ .  Whatever you like,
but you need five of them..  

The answer is c.  the soft ware is unable to you because it is open for the public to use.