OA is B.
1. perfumes made with synthetic ingredients, so in the second subclause you need this relationships classic fragrances....flowers and natural essences.
Although today it is cost-effective to make perfumes with synthetic ingredients, they used to make the classic fragrances from flowers only
and other natural essences.
A) they used to make the classic fragrances from flowers only
[THEY represents whome? Incorrect and flowers only is misleading and doesnt fit with the last non-nderlined part. Incorrect
B) the classic fragrances used to be made only from flowers [Correct]
C) the classic fragrances used to be made by them
only from flowers [by them - awkward. Incorrect
D) the classic fragrances used to be made from flowers only
E) only flowers used
to make the classic fragrances [This is reverse of the introductory part. You need a verb (for passivity) before USED. Incorrect