When did hawking notice clumsiness for the first time?

Stephen Hawking, the popular cosmologist, author, and physicist, was diagnosed with MND and got disabled at a very tender age. He first noticed the clumsiness when he was in his final year at Oxford University. This clumsiness included his sudden fall off from stairs and problem in arguing. This was followed by slurring of his voice and eventually, the medical test revealed that he is suffering from MND at the tender age of 21.

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i think the answer would mist likely be an adjective clause, because unhappy is an adjective.