thE purposE oF gEorgE spiliCh's ExpErimEnts is ______.
A．to tEst whEthEr smoking hAs A positivE EFFECt on thE mEntAl CApACity oF smokErs
B．to show how smoking DAmAgEs pEoplE's mEntAl CApACity
C．to provE thAt smoking AFFECts pEoplE's rEgulAr pErFormAnCE
D．to FinD out whEthEr smoking hElps pEoplE's short-tErm mEmory