The quantifiers few and a few, and little and a little seem nearly identical but they are actually quite distinct. These expressions show the speaker's attitude towards the quantity he is referring to as either positive or negative.
Positive Attitude:
A few (for countable nouns) and A little (for uncountable nouns) describe the quantity in a positive way, implying that although the speaker may not have much, he has enough. Eg:- I have got a few friends. / I have a little free time on Fridays.
Negative Attitude:
Few (for countable nouns) and Little (for uncountable nouns) describe the quantity in a negative way. They may actually indicate a total lack of the noun, but are more polite than saying so directly. Eg:- Few people visited him in hospital. / I have little time for TV.
This sentence states that there were some flowers in the vase. Again, flower is a countable noun. Hence, Option A, 'a few' is correct.