Definition: 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.
Input: Question: Which of Messner's teachers at the University of Munich was older? Passage:After Meissner’s abitur at the Humanistisches Gymnasium, in 1910, he began the study of physics and mathematics at University of Tübingen. After three terms, he went to the University of Munich as a student of the experimentalist Wilhelm Röntgen and the theoretician Arnold Sommerfeld. After one year at Munich, he returned to Tübingen to be able to study spectroscopy with Friedrich Paschen. While still a student in 1914, Meissner was able to prove the existence of oxygen lines in the solar spectrum. He was awarded his doctorate in 1915, on a thesis with the title Interferometrische Wellenlängenbestimmung im infraroten Spektralbereich. In 1916 he became an assistant to Edgar Meyer at the University of Zurich, under whom he completed his Habilitation, in 1918, with the Habilitationsschrift title Untersuchungen des Neonspektrums. The following year, he married the Polish physicist Doctor Janka Kohn.
 Links: a. Habilitation b. Ludwig Maximilian University of Munich c. University of Tübingen d. Wilhelm Röntgen
Output:
d