Hello
Let's try to find the relative or specific antecedent.
the scientist knew that something had to be done to keep the discovery secret or, he (the scientist) would lose his opportunity to announce it (the discovery) first.
As you can see, "he" and "it" does have an antecedent. Therefore, the correct answer is B: something.
Something is an indefinite pronoun; and, in this case, it does not have a specific antecedent.
Hope his helps
