Select the most appropriate option that can substitute the highlighted segment in the given sentence.
"The most effective way to enhance your vocabulary is to look to unknown words in a dictionary."

The correct replacement is (b) "look up."
Explanation:
· "Look up" means to search for information in a reference source, which fits the sentence.
Other Options:
· (a) "Stand against" – Incorrect, means to oppose.
· (c) "Set by" – Incorrect, not a correct phrase in this context.
· (d) "Write off" – Incorrect, means to dismiss something as a loss.
Corrected Sentence:
· "The most effective way to enhance your vocabulary is to look up unknown words in a dictionary."
Example Sentence:
· "I always look up difficult words in the dictionary."