Answer: Option (d) is the correct answer.
Step-by-step explanation:
Article's help people know about the advantages or disadvantages of the product or topic for which it is written.
Basically an article provides an overall scenario about a situation or thing so that readers can decide themselves whether they are in favor or against the thing on which article has been written.
Therefore, we can conclude that out of the given options, to get the reader to understand the two types of signals is most likely the author’s motive for writing the article.