The answer to your question is A., Standing in the line.
The mood is conveyed by the choice of words as in simple casual speech or difficult, more formal words, the tone of the writers is something to consider also
I would say the author uses irony in this passage that remembering his mother makes him not happy but miserable which may be the opposite of what is expected but he would rather suffer this than be happy in forgetting her as this latter feeling would be expected to make him sad.
