Final answer:
The word 'difficult' is an antonym(option b) to the phrase 'this is a simple exercise' because it suggests that something is challenging, which is the opposite of simple or easy.
Step-by-step explanation:
In response to the student's question, the word difficult serves as an antonym to the phrase 'this is a simple exercise.' An antonym is a word that has a meaning opposite to that of another word.
When we describe something as simple, we suggest that it is not complicated or challenging, which could be understood with little effort. However, the word 'difficult' implies that something requires much effort or skill to do or understand. Therefore, in this context, the word 'difficult' is used to contrast the ease implied by 'simple,' making it an antonym.
Understanding how antonyms work can greatly enhance a student's vocabulary and comprehension skills. For instance, when learning new words, recognizing their antonyms can provide a deeper grasp of their meanings. This knowledge can be very useful, especially when tackling various subjects across a student's academic journey, including preparing for standardized tests or engaging in creative writing.