This is certainly the case, but ____ it is a mistake or not I don’t know. 
#73119
A
if
B
even though
C
whether
D
that
推荐题目
The man ___ was an old classmate of mine.
#72345
A
you just talked to him
B
who just talked to
C
you just talked to
D
whom you just talked
No doubt ________ he knew the news.
#69991
A
that
B
if
C
whether
D
but