Lucas wants to include an explanation clue in his sentence. How should he do that? He should add words that are similar to the unknown word.
He should add words that are the opposite of the unknown word.
He should add words that give information about the unknown word.
He should add words that are in the same group as the unknown word.

He should add words that are similar to the unknown word.

Explanation:

The inclusion of explanation clues in a sentence is with the intention of giving a more and understandable explanations for any unknown word used. This allows the readers to understand the words that the writer used.

So, for a writer to provide explanation clues, he/she must add words that are similar to the unknown word. This is because similar words will help enable the reader to understand the word(s) used and also help them understand the whole sentence clearer.  Therefore, Lucas should add words similar to the unknown words.

Thus, the correct answer is the first option.

- "a nonrestrictive clause functions as a modifier to a noun (that is an object, person or concept). these clauses can be described by the following three options: it is set off by comas, it contains a subject and a verbs and it adds nonessential information to the sentence.

for example, in "here is bill gates, who confounded microsoft software company" we can identify "who confounded microsoft software company" as a nonrestrictive clause modifying the noun bill gates. this clause can be describes as a nonrestrictive clause because it is separated by a comma, it adds nonessential information to identify who bill gates is and it must contain both a subject (who) and a verb (confounded)."