Option B is the correct answer because ‘regularly’ means ‘to
do something frequently’. Thus, ’regularly’ is the most appropriate adverb, which modifies the verb exercise, to
complete the meaning of this sentence.
Option A is incorrect because ‘regular’ is an adjective and it is grammatically
incorrect for this sentence.
Option C is incorrect because ‘regularize’ is a verb and it is not the
grammatically appropriate word for this sentence.
Option D is incorrect because ‘to regulate’ is a verb and it is grammatically
incorrect for this sentence.