So going according to the hint and the information, we will dissect all the given options to reach the most suitable bone in this case. Option A is' hinder'. The word means being at the end or on the aft part. This word has a meaning that's contrary to the meaning of the word vanguard. This also meets the conditions mentioned in the hint. thus, option A can be the correct answer. Option B is ‘ Front ’. This word means to be in the commanding position. This word has a meaning analogous to the word vanguard. thus, the word front is the reverse of vanguard and not an antipode. therefore, option B is incorrect. A troop refers to a unit of army or group of dogfaces that are endless. This word is nowhere related to the word vanguard. thus, this word is neither reverse nor antipode of the word vanguard. therefore, option C is also wrong. Echelon means the rank or position at a place be it an association, society or others. This word also has meaning in military terms but indeed in that case, it isn't related to the meaning of the word vanguard. thus, option D is also incorrect. therefore, option A is the correct answer.