Question:
Which employer did Karen Keskulla Uhlenbeck work for in May, 1971?

Context:
 Karen Keskulla Uhlenbeck works for University of Texas at Austin from Jan, 1988 to Jan, 1988. 
 Karen Keskulla Uhlenbeck works for University of Illinois at Chicago from Jan, 1976 to Jan, 1983. 
 Karen Keskulla Uhlenbeck works for University of Illinois at Urbana–Champaign from Jan, 1971 to Jan, 1976. 
 Karen Keskulla Uhlenbeck works for University of Chicago from Jan, 1983 to Jan, 1988.

Answer:
University of Illinois at Urbana–Champaign