Final answer:
In 'Flowers for Algernon's' Progress Report 9, Charlie's 'tripping' on April 20 refers to his mental and emotional turmoil as he grapples with his rapidly increasing intelligence from the experimental procedure conducted on him.
Step-by-step explanation:
In the context of Flowers for Algernon, which is the narrative source from which Progress Report 9 is derived, Charlie was 'tripping' on April 20 because of the mental and emotional turmoil he was experiencing as a result of the rapidly increasing intelligence from the experimental procedure performed on him. The term 'tripping' here refers metaphorically to fluctuations in perception and emotional cognition, not an actual physical fall. During this period, Charlie experiences drastic changes in his intellect that confuse and frighten him, causing him to 'trip' mentally as he tries to adapt to his changing circumstances.
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