Why did the speaker show us the picture about a swimmer, a rowboat, a sailboat, and a tugboat?

A、Toshowwhatmayhappentothedevelopmentofmedicine.;
B、Toshowhowmanydifferentwaystocrossthesea.;
C、Toteachustothinkoutsidetheboxwhendevelopinganewmedicine.;
D、Toteachusbuildingabridgeisnotthebestway.