—Tom, you look puzzled.Do you understand it?
—Yes.I __________ another problem just now.
A.have thought of B.had thought of
C.was thinking of D.am thinking of
—Tom, you look puzzled.Do you understand it?
—Yes.I __________ another problem just now.
A.have thought of B.had thought of
C.was thinking of D.am thinking of
C