(A)Howbiochemicalchangesoccurinthehumanbrain.
(B)Whypeopleshouldkeepactivenotonlyphysicallybutalsomentally.
(C)Howintellectualactivitiesinfluencebrain-cellhealth.
(D)Whypeopleshouldreceivespecialmentaltrainingastheyage.
参考答案