The correct option is C Timid
The given word 'bold' means 'confident, someone who shows courage and is fearless.
'Timid' means the lack of this courage or confidence. It is opposite in meaning to 'bold', in other words, it's an antonym. Hence option B is correct.
'Brave' means 'to show courage', it is synonymous in meaning to 'bold'.
'Incredible' means 'unbelievable, marvelous', it is neither similar in meaning nor opposite in meaning to 'bold'.
'Courageous' means 'fearless, brave', it is also synonymous to 'bold'.
Hence options A, C and D are incorrect.