To answer this question, let's go through each option to understand why it is correct or incorrect:
Option A) impressiveness - This option is incorrect because "relent" does not mean impressiveness. "Relent" means to become less severe or to soften in attitude, opinion, or tone.
Option B) become less severe - This option is correct because "relent" means to become less severe or to soften in attitude, opinion, or tone. This is the correct definition of the word.
Option C) admit fresh air into to replace stale air - This option is incorrect because "relent" does not have anything to do with admitting fresh air or replacing stale air.
Option D) causing great fear - This option is incorrect because "relent" does not mean causing great fear. It means the opposite, to become less severe or to soften.
The correct answer is B) become less severe. This option is correct because it accurately reflects the meaning of the word "relent."