In this task, you're given a question, a context passage, and four options which are terms from the passage. After reading a passage, you will get a brief understanding of the terms. Your job is to determine by searching and reading further information of which term you can answer the question. Indicate your choice as 'a', 'b', 'c', or 'd'. If you think more than one option is plausible, choose the more probable option to help you answer the question.

Question: Which colleague Neugebauer collaborated with at Mount Wilson Observatory is the oldest? Passage:Neugebauer was active in infrared astronomy, and played a leading role in infrared studies of the planets. In additionand largely through his activities with the Infrared Astronomical Satellite (IRAS) and the Infrared Processing and Analysis Center (IPAC)he led both ground- and space-based infrared studies of the stars, the Milky Way and other galaxies. Observations by him and his colleagues at Mount Wilson and Palomar observatories revealed thousands of infrared sources in the sky, and afforded the first infrared view of the galactic center. Together with Robert B. Leighton, he completed the Two-Micron Sky Survey, the first infrared survey of the sky, which cataloged more than 5,000 infrared sources. Together with Eric Becklin, he discovered the BecklinNeugebauer Object, an intense source of infrared radiation in the Orion Nebula that is one of the brightest objects in the sky at wavelengths less than 10 micrometres.
Links: a. Star b. IRAS c. Robert B. Leighton d. Two-Micron Sky Survey
c