The correct option is C Speedy
A synonym is a word that is similar in meaning to another.
The word 'swift' means something happening quickly or promptly, for example, 'a miraculously swift recovery'.
From the options, 'speedy' means 'done quickly, moving quickly', for example, 'a speedy recovery'. It is synonymous with 'swift', both mean quick. Hence option B is correct.
'Move' means 'to change position', for example, 'Please move over there.' It refers to a change in position or direction whereas 'swift' refers to speed or pace. Hence option A is incorrect.
'Leisurely' means an unhurried manner, relaxed manner. It is the opposite of 'swift', it is an antonym; hence option C is incorrect.
Similarly, 'sluggish' means 'slow-moving, inactive'; it has an opposite meaning to the given word, hence option D is incorrect.