问题
选择题
—When did your cousin begin to show his interest in medicine?
—It was a Saturday ___ she noticed her uncle experimenting on a frog in his lab.
A．that
B．what
C．when
D．which
答案
答案：C
本题修饰名词Saturday为定语从句，先行词Saturday为时间，关系词应该用when，故本题C。