The correct option is D To be less than or below
Option C is the correct answer because 'to fall short of' means 'to fail to reach a certain amount or standard'. Thus, option C is the most appropriate meaning of the given idiom.
Option A is incorrect because 'to pick a quarrel' means 'to quarrel with' Thus, option A is not the appropriate meaning of the given idiom.
Option B is incorrect because 'I beg to differ' means 'to disagree with'. Thus, option B is not the appropriate meaning of the given idiom.
Option D is incorrect because 'to deteriorate' means 'to become worse'. Thus, option D is not the appropriate meaning of the given idiom.