Answer: Because of automatic processing
Explanation: In the case of Sharon, It's an automatic space processing. Automatic processing does not require effort, i.e. focusing on given activity. It's about unconscious encoding, which in the Sharron case refers to the space, because she effortlessly returned to the place in the book she left when she heard that the phone was ringing. It means that automatic processing does not require additional thought resources, nor does it interfere with existing, concurrent thought processes. Generally automatic processing can also apply to time and frequency, as well as to well-remembered things, information.