Answer: A is correct. But I must add ....that (A) is a so-called "scientific ideal" (typical for 19th century) and we know that it cannot be reached. Historians are human beings and human beings are - always, always, always - subjectives. In 19th century there was a belief that "science" to be science should produce "laws"/"natural laws" (law = rule that is valid absolutely, always without exception). This ideal of absolutely objective science is no more accepted or is - at least - relativized (especially in humanities, social sciences where subjectivity plays a significant part.
Explanation: A = it is still a goal, but it is a traditional goal linked with 19th century "scientific historiography". Today we are aware that historians are people with their subjectivity.