—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