Optimismhasapositiveeffect________people"sphysicalandmentalhealth，________whichI"mveryconvinced．（　　） --优优班--学霸训练营

Optimism has a positive effect ________ people"s physical and mental health，________ which I"m very convinced．（　　）

A．on； of

B．to； in

C．at； at

D．on； at

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难度：较易

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