The correct answer is B. Ancient
Step-by-step explanation:
In grammar, the word capitalization refers to writing the first letter of a word in uppercase while leaving the rest of the letters in lowercase. This according to grammar use should be applied to the first word of a text or after a period and to proper names which besides the specific names of people and places includes time periods or important events in history such as the World War I or the Civil War, including adjectives and similar directly related to them. This means in the case of the sentence " Professor Singh is a specialist in ancient Chinese History" the word "Ancient" should be capitalized as this is part of the proper noun "Ancient Chinese History" and therefore the word with a capitalization error is "Ancient".