Which line from "forgetfulness" best contributes to a humorous tone? a. decided to retire to the southern hemisphere of the brain b. whatever it is you are struggling to remember c. no wonder the moon in the window seems to have drifted d. well on your own way to oblivion where you will join those

The poem by Billy Collins describes how a person forgets certain stuff, generally considered with learning. The author introduces the novel as an example that how it is going to be forgotten piece by piece after certain times. Applying personification in the third stanza in the example of planets and irony in the last stanza where the author concludes that the memory is bound to forget even if you try to remember and not to forget. The lines  the memories you used to harbor  decided to retire to the southern hemisphere of the brain, have got a humorous tone. The author makes an humorous reference to the memory and recalling function of the left brain that it is no longer functioning anymore. The correct answer is A.