28. ---- Who told you my email address?
题型：选择题
问题：
28. ---- Who told you my email address?
---- I don’t remember clearly. It _______ Karen.
---- It _______ Karen. She doesn’t know my email address.
A．may have been; can’t have been
B．must have been; mustn’t have been
C．may have been; must have been
D．must have been; mustn’t be