函数$f\left(x\right)=\sin \left(\omega x+\phi \right)\left(x\in R\right)\left(\omega >0,\left|\phi \right|<\frac{\pi }{2}\right)$的部分图像如图所示，如果$x_1,x_2\in \left(-\frac{\pi }{6},\frac{\pi }{3}\right)$，且$f\left(x_1\right)=f\left(x_2\right)$，则$f\left(x_1+x_2\right)=$(       )

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    Mr Turner teaches in a middle school. He's friendly to his students. And he is always strict with himself. He often tells his students to be polite and to do their best to help the persons who are in trouble.

    One Monday morning, Mr Turner didn't go to work and went to see Mr White who was ill in hospital. As something was wrong with his car, he had to take a bus. At first he easily found a seat, but soon plenty of people got on the bus and it was very crowded. Some of them had to stand. Mr Turner looked around and saw a woman standing behind. He stood up and made room for her. The woman said nothing and sat down. Her behaviour made Mr Turner unhappy.

    "It's necessary for her to be taught how to be polite," he said to himself. Then he asked, "What did you say, madam?"

    "I didn't say anything, "answered the woman.

    "I thought you said 'Thank you!"'

    When the woman heard this, her face turned red.