Who killed julia stoner in the story of the speckled band ?

i think its d, but grammarly says none

explanation:

ian mortimer in his book "the time traveller's guide to elizabethan england" uses a narrative in his style, which successfully conveys a clear description of the life in england in the 16th century. he writes in second person, which makes it comfortable to reader and easy to understand, he captures the readers attention with views of the landscape, the streets, the people including rich and poor. he also depicts some cultural traits from how people behave, eat or what they wear. his descriptions range from the social, economical, the political power to the examples of the life of common people. it could be tell that this book is about social history rather than a   novel.