Select the word-pair that best represents a similar relationship to the one expressed in the pair of words given below. (The words must be considered as meaningful English words and must not be related to each other based on the number of letters/number of consonants/vowels in the word.)
Plain : Austere

Given:

The pair Plain : Austere.
A) Clean : Sterile → Sterile is an extreme form of Clean (in terms of purity and lack of germs).  (Possible)
B) Lonely : Gloomy → Lonely and Gloomy are related, but not in an extreme degree of the same concept (Not the same pattern)
C) Neutral : Detached → Neutral means unbiased, while Detached means emotionally disconnected. These are related but not in the same degree pattern.  (Not a perfect match)
D) Abandon : Barren → Abandon means to leave, Barren means infertile. These words are unrelated in the required sense. (Not the same pattern)
Since Sterile is a more extreme form of Clean, just as Austere is a more extreme form of Plain, the best answer is (A) Clean : Sterile​​