The correct answer is D. Not attractive
Step-by-step explanation:
In the sentence "Although Tiffany liked the style of the dress, she thought it was unflattering when she tried it on" the unknown word "unflattering" is used to describe the negative feeling of Tiffany towards the dress while she tried, which is the opposite to her first impression about the dress "Tiffany liked the style of the dress". This means the word unflattering describes despite the dress had a style Tiffany like when she wore it she thought the dress was not favorable or that it mainly was not attractive, which is the opposite to the word flattering. Therefore, the meaning of "unflattering" in this sentence is "not attractive".