Today I took part in the English singing competition of our school. Most of the singers and audience have been there when I arrived at the ball. See the large audience, I started to feel little nervous. After some times, it was my turn to sing. When the host read my name out, the audience burst into a great cheer, and my heart began to beat really fastly. The song I sing was Country Road, that is a very famous piece of American country music. I had practiced for it many times, and I didn’t think I had done a very good job. Anyway, I was still very excited because of participating was the most important thing to me.

病历摘要：肺结核患者，女性，51岁。体检发现左上肺高密度结节。查体：双肺呼吸音清，未闻及干湿性啰音。心脏无异常。行胸部CT平扫。

2.诊断依据是什么？