adjective
1
BAD : She began to think she was becoming mad.
GOOD : She began to think she was going mad.
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go mad (NOT become ) =: 'Eventually, rejected by Hamlet, Ophelia goes mad and drowns herself.'
2
BAD : I've always been mad for tennis.
GOOD : I've always been mad about tennis.
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be mad/crazy about sth (NOT for ) = (informal) like something very much: 'Why are so many people crazy about computer games?'