{$mEDiAurl}
whAt DoEs thE proFEssor mEAn whEn hE sAys this:A．hE is CErtAin thE stuDEnts know thE mEAning oF thE worD、
B．hE wAnts to mAkE surE thAt stuDEnts hAvE unDErstooD his ExplAnAtion.
C．hE is worriED his stuDEnts hAvE not CovErED All thE mAtEriAl so FAr.
D．hE wAnts to ChECk whEthEr his stuDEnts hAvE stuDiED thE mAtEriAl so FAr.