问题
g messages by telephone hasbecome _______ second most popular way of exchanging of New Yeargreetings, according to _____ research by China Daily
A:whom I know have learned
B:whom I know has learned
C:I know who has learned
D:I know who have learned
B:whom I know has learned
C:I know who has learned
D:I know who have learned
正确答案是：
