Choose the ONE that is a synonym for the word：plethora A: overplus B: embarrassment C: few D: extreme

________________ are more commonly known as 'mind-enhancing drugs' or 'smart drugs'. A plethora of drugs are already known to cause a variety of effects on the brain, e.g., the stimulatory action of caffeine.

The most visible result of （this buoyant ）market in both centers is a plethora of new multi-storey commercial and residential buildings.（） A: positive` B: active C: passive D: negative