The correct answer is the following: <em>option B</em>. In order to avoid the unnecessary shift in verb tense through the paragraph, the second sentence should be <em>"They had been searching for it for years". </em>The original paragraph starts with the sentence "The scientists were excited after they made the discovery" and then it goes to the second sentence that states " They have been searching for it for years". The opening sentence is written using the simple past tense, and in the second one the narrator uses the present perfect verb tense. This is an unnecessary shift in verb tenses, as it is always advised to use the same verb tense throughout a paragraph or story so that it is coherent. That is why the best option is to use the past perfect verb tense in the second question, to keep both a sense of coherency and for the message to not be altered.
