Who among the following was a major advocate of oral history?

The correct option is Paul Thompson.

Explanation:
Paul Thompson is a British sociologist and researcher who is widely recognized as a pioneer and major advocate of oral history. He played a foundational role in establishing oral history as a respected academic methodology. His seminal work, The Voice of the Past: Oral History (first published in 1978), is a classic text in the field that argues for the inclusion of the voices of ordinary people to create a more democratic and comprehensive understanding of the past.

Why the other options are incorrect:
- Sylvia Plath was an acclaimed American poet and novelist, best known for her confessional poetry and her novel The Bell Jar, rather than historical methodology.
- Esther Greenwood is the fictional protagonist of Sylvia Plath's semi-autobiographical novel The Bell Jar, not a real-life historian.
- Carolyn Steedman is a prominent British historian and academic known for her work in social history, cultural studies, and autobiography (such as her book Landscape for a Good Woman), but she is not the primary figure associated with the pioneering advocacy and theorization of oral history in the way Paul Thompson is.