In the United Kingdom, you either apply directly to the college of the subject you want to study, or in the case of undergraduate programs, you apply through a centralized system which allows you to apply to several colleges at once. This system is called the __________, or UCAS. （ ）
选项：

A:Universities and Colleges Admissions Service
B:Universities and Colleges Advice Service
C:Universities and Colleges Admissions Standard
D:Universities and Colleges Advice Standard