Answer:
The answer is the book.
Step-by-step explanation:
A simple subject is a single noun or pronoun connected to a verb. A simple subject is a noun. Nouns are a person, place, or thing.
An example of a simple subject is "Dogs are good pets." Dogs is the simple subject; it is the noun that the sentence is about.
Book is the simple subject; it is the noun that the sentence is about.
Hence, the answer to this question is, the book.