The word "courageous" means someone who lacks fear or is not deterred by danger. It is an adjective which can be used to describe the attribute of a person or an act (" her courageous confession led to the arrest of the fugitives"). From the given options we can infer that option C is the antonym of courageous.
The word "fickle" means something that changes frequently or is erratic, hence A is not a viable option.
Insipid means bland or lacking flavour. It can also mean dull or spiritless, hence option B cannot be an antonym for courageous.
Option D "fearless" is a synonym of courageous, hence is an incorrect option.
The word "timorous" means showing or suffering from nervousness, it is an adjective meaning someone who lacks courage or is faint-hearted especially in the face of danger. Thus option C is the antonym of courageous. Usage of timorous: The timorous cat retreated behind the closet whenever it heard a voice that it didn't recognize.