Which of the following is NOT a reason for the Mona Lisa's myste

Which of the following is NOT a reason for the Mona Lisa's mysterious smile?
A、It represents the ideal of feminine beauty during the Renaissance.
B、It suggests that the sitter was unhappy with the portrait.
C、It reflects Leonardo's technique of sfumato, giving a soft and hazy effect.
D、It has been interpreted as a sign of hidden knowledge or secrets.
【正确答案】:B
【题目解析】:It suggests that the sitter was unhappy with the portrait.