Answer:
C). Sentence Fragment.
Step-by-step explanation:
A sentence fragment is described as an incomplete sentence; a phrase or clause that is punctuated and capitalized like a sentence but does not constitute a complete grammatical sentence. It is usually caused by the failure to include a subject and a verb, or as the result of beginning a sentence with a subordinate conjunction or relative pronoun.
The given is a 'sentence fragment' error as it conveys a partial meaning. It is incomplete as it begins with a subordinating conjunction('if...know') and without accomplishing a complete meaning it ends abruptly. A dependent clause must always be followed by an independent clause to accomplish its meaning but here, it is immediately followed by a dependent clause beginning with another relative clause('how...end'). Thus, option C is the correct answer.