Concept:The comparative form of an adjective (
milder,
taller,
better) is used when comparing exactly two things. For three or more, the superlative (
mildest) is used.
Solution:The sentence uses "milder", the comparative, so exactly two fragrances are being compared.
Therefore the blank must be "two": "Which of the two fragrances is milder?"
B. "one" makes no comparison at all; you cannot ask which of one thing is milder.
C. "most" and D. "all" point to more than two, which would need the superlative "mildest".
Key point: Comparative (-er) goes with two; superlative (-est) goes with three or more.
Answer:Option A (two)