Definition: In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].
Input: Washington (CNN) The Environmental Protection Agency's acting science adviser is retiring, he told CNN Saturday. Robert Kavlock, who also serves as acting assistant administrator for the Office of Research and Development, will be leaving his position effective November 3, he said. He initially declined to explain the reasons behind his retirement, but in a follow-up email to CNN, he said he had worked at the agency for four decades "so it was not an early retirement." He added that "the time was right to go for a variety of reasons." Kavlock, who has more than 33 years of scientific experience, previously directed the National Center for Computational Toxicology within ORD. He joined the EPA in 1977, according to his biography on the agency's website.Robert Kavlock also serves as acting assistant administrator for the Office of Research and DevelopmentKavlock has more than 33 years of scientific experience 
 Question:In May, _ dismissed half the scientists who were serving on the executive committee of a key EPA science review board that provided guidance on air and water quality.

Environmental Protection Agency