{$mEDiAurl} why DoEs thE proFEssor sAy this:
A、to show thAt thE stuDEnt hAs rEminDED him oF AnothEr iDEA、
B、to shiFt thE FoCus oF thE DisCussion BACk to thE mAin topi
C、
C、to inDiCAtE thAt thE ClAss might run ovEr timE.
D、to ExplAin A point just mEntionED By thE stuDEnt.