Answer: A and B
The tone of a text is the attitude that a writer has toward a subject or an audience. For example, a text can be cheerful, sad, comic or sarcastic.
The most common way to convey the tone is through the use of words. In this example, "celebrate" and "sing" generally have a cheerful, positive meaning. Therefore, we can assume that the tone of the piece is a happy one. On the other hand, "belonging" and "assume" are neutral words, and they do not convey any feeling by themselves.