Adjectives are the words that define/explain nouns or pronouns. For example: Roshni is pretty. Here, 'Roshni' is the noun and 'pretty' explains how she is, hence 'pretty' is the adjective.

Adverbs are the words that describe action words (verbs). For example: Ram fought bravely. Here, 'Ram' is the noun and 'fought' is the verb. 'Bravely' describes how he fought, hence it is the adverb.

Option A - 'I did the homework complete by myself.' Here, 'complete' is a verb whereas we need an adverb to describe how the work is done. Hence, option A is incorrect. 

Option B - 'I did the homework to completely by myself.' Here, 'to completely' is used incorrectly as the marker 'to' is always accompanied by the verb in its original form. Hence, option B is incorrect. 

Option D - 'I did the homework completed by myself.' Here, 'completed' is used as a verb and not as an adverb. Hence, option D is incorrect. 

Option C - 'I did the homework completely by myself.' Here, 'completely' is used as an adverb to describe the way the homework is done. Hence, option C is the correct answer.