**B. She was reading a book**

Suguna was engaged in the activity of reading a book when she heard someone at the door. This implies that she was focused on the book and her attention was diverted by the sound of someone at the door. Let's explore this answer in more detail.

When someone is reading a book, they are usually engrossed in the story or information presented in the text. Reading requires concentration and attention to comprehend the content and follow the narrative. It is a solitary activity that often takes place in a quiet environment, allowing the reader to immerse themselves in the book's world.

By stating that Suguna was reading a book when she heard someone at the door, it suggests that she was deeply involved in the reading process. She might have been sitting or lying down, holding the book in her hands, and turning the pages as she progressed through the text.

The act of reading requires mental engagement, as the reader needs to decode the words, understand their meaning, and interpret the ideas presented by the author. This cognitive process demands focus and concentration, as the reader's mind is actively processing the information in the book.

When Suguna heard someone at the door, it interrupted her reading session. The sound of the doorbell or knocking would have caught her attention, causing her to momentarily pause her reading and divert her focus towards the source of the sound.

In summary, Suguna was reading a book when she heard someone at the door. This answer suggests that she was deeply engrossed in the book, demonstrating her interest in reading and her dedication to the activity.