Which of these best describes the tone of the wife's lament? A. Contentment B. Longing C. Confusion D. Blitheness

I would say the correct answer is B. longing.

In this poem, the wife is lamenting because she is separated from her husband - for a very long time. She misses her husband and wants to be reunited with him, so she is definitely not content or blithe about her situation (blithe means happy). She is not confused either - she knows that she wants her husband back.