S.T. Colerige's 'Khan' is a poem about

S.T. Coleridge's 'Kubla Khan' is a notable English Romantic poem. The content of the poem is a complex blend of various elements, but it's primarily known for its portrayal of an opulent dream world created by the title character, Kubla Khan. However, the dream world is also associated with a sense of foreboding and an eerie presence, which is why the correct answer is Option B: the world of demon lovers.

In the poem, Coleridge describes the palace that Kubla Khan orders to be built in a place called Xanadu. The palace is surrounded by 'gardens bright with sinuous rills' and 'forests ancient as the hills', but beneath it runs a tumultuous river that leads to a 'lifeless ocean'. This dichotomy between the beautiful, peaceful garden and the tumultuous, lifeless ocean beneath it is often interpreted as a representation of the duality between good and evil, or between reality and the supernatural.

In the second part of the poem, Coleridge introduces a damsel with a dulcimer, who is described as a 'woman wailing for her demon lover'. This introduces the element of the supernatural and the theme of forbidden love, which is why the answer is 'the world of demon lovers' rather than simply 'a dream world'. The damsel and her song also symbolize the power of the poetic imagination, a common theme in Romantic literature.

The other options, such as 'the river Alph', 'a sunless sea', and 'sunny spots of greenery', are all elements present in the poem, but they do not capture its overall theme and content as accurately as 'the world of demon lovers' does.

To understand this complex poem more deeply, it's recommended to read it multiple times and refer to detailed analyses in literature textbooks or reputable online sources.