"The Lake Isle of Innisfree" by W. B. Yeats is a/an 

The question is asking about the type of written work "The Lake Isle of Innisfree" by W.B. Yeats is. The options provided are "play", "elegy", "sonnet" and "poem". The correct answer is "poem". To explain it in simpler terms, "The Lake Isle of Innisfree" is a written piece by W.B. Yeats and it falls under the category of a "poem". A poem is a type of written work characterized by rhyme, meter, and often contains literary devices such as symbolism or metaphor. So, "The Lake Isle of Innisfree" is a specific example of a poem written by W.B. Yeats.