Answer:
A
Step-by-step explanation:
Try to eliminate some of the choices.
B. "A serious tone"; people usually associate serious tones with anger, disappointment, or any other negative feeling. However, we don't want Maria to be angry, so eliminate this.
C. "Emphasis on the words Sir Toby"; the sentence would then read: "By my troth, Sir Toby, you must come in earlier o'nights". When reading it and emphasizing "Sir Toby", it makes it sound like Maria is blaming Sir Toby, which again lends a kind of angry tone to it. So, eliminate C.
D. "Emphasis on the word must"; the sentence would then read: "By my troth, Sir Toby, you must come in earlier o'nights". When reading it and emphasizing "must", it makes it sound like Maria is exasperated with Sir Toby and is almost ordering him to come in earlier. Just like before, this makes Maria sound angry. So eliminate this.
Thus, the answer is A; if Maria speaks in a playful tone, this indicates that she is content, not angry.
Hope this helps!