Why can't write a SOME order?

[Thalia]

English Language Tests, Intermediate level

ESL/EFL Test #249 "Few, a little and some (1)", question 4

I can't go right now because I still have a ......... orders to fill by 5 o'clock.

(a) few
(b) little
(c) some

English Language Tests, Intermediate level

ESL/EFL Test #249 "Few, a little and some (1)", answer 4

I can't go right now because I still have a few orders to fill by 5 o'clock.

Correct answer: (a) few

Your answer was: incorrect
I can't go right now because I still have a some orders to fill by 5 o'clock.
_________________________

i think orders are countable noun. Why can't write a SOME order?
please explain this to me.
thanks in advance

Thalia

[Conchita]

We can say either 'a few orders' or 'some orders', but not 'a some orders'.