The correct answer is B. A student becoming bored during a lecture
Step-by-step explanation:
The main idea or what a literary work is about can be identified by understanding the topic, situation or issue the short, story, poem or novel convers and the main idea the details describe. In the case of Whitman's poem "When I heard the learn'd astronomer" the author or narrator of the poem describes what he sees and hears while he is in a lecture including the different diagrams and charts that are part of it, while he is feeling tired and sick. However, at the end of the poem, the narrator can finally make sense of the astronomer lecture as he looks at the sky. This implies the details in this poem shows the situation of the narrator during the lecture and after it and therefore, the main idea of this poem or what the poem is about is "a student becoming bored during a lecture" but finally finding the sense of it through the experience.