Answer:
Fourth Option “A perfect taste made possible by the most brutal labor.”
Step-by-step explanation:
Author's main purpose of this excerpt is about difficulties, problems and labor involved with the production of sugar. He also points out that sugar is sweeter than honey. Both these purposes are fulfilled in this quotation i.e. “A perfect taste made possible by the most brutal labor.” A perfect taste for sweeter taste of sugar, and the most brutal labor for difficulties and labor put in for the production of sugar.
First, second and third options are not correct because they support only one part of the author's main purpose i.e. either difficulty or taste.