Answer:
A. What types of wild horses exist in the United States?
Step-by-step explanation:
The answer to the above question would help Carlos to specify his research to the types of wild horses existing in the United States. This question would narrow down the topic "wild horses" which is too vast to research and help him focus his attention towards a particular area which would lead to an impressive paper. While writing an influential paper, it is very significant to specify your topic as it not merely provides the lead to begin the research but also assists in selecting the source and shifting the attention towards the research in a more centralized manner. Some may argue that it confines the researcher to a particular topic but it helps them in being more specific and impressive, instead of being diverse and manipulated.