All of Agency X's customers are U.S. citizens. Some of Agency Y's customers are not U.S. citizens. Based on the above information, which of the following statements must be true?
A. Some of Agency Y's customers are not customers at Agency X.
B. None of Agency Y's customers are customers at Agency X.
C. Some of Agency Y's customers are customers at Agency X.
D. None of Agency X's customers are customers at Agency Y.
E. Some of Agency X's customers are not customers at Agency Y.