adjective
1
BAD : I'm afraid I speak English very bad.
GOOD : I'm afraid I speak English very badly.
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Bad is an adjective: 'I tried to ignore the child's bad behaviour.'
Badly is an adverb: 'The child behaved very badly indeed.'
2
DUBIOUS : Of course, there are also bad things about living in a city.
GOOD : Of course, there are also disadvantages to living in a city.
DUBIOUS : It's a bad thing that the population is increasing so quickly.
GOOD : It's unfortunate that the population is increasing so quickly.
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The phrase bad thing/s is generally over-used and often sounds unnatural.
See also THING (↑ thing )