How does a photography teacher choose photos?

This question is not very interesting. In photography, the tone is generally divided into 10, from 0 to 9, where 0 is all black and 9 is all white. Usually, the gray scale of 18% measured by the camera photometry element is five tones, and each level differs by one exposure.

Because a photo is composed of different levels of tones, it is usually divided into high-key, low-key and intermediate tones. I understand what your teacher means: Indoor Band Four uses evaluation metering and then exposure compensation-1; Outdoor 7-level tone is evaluated by photometry and then exposure compensation is +2.

As for the combination of aperture and shutter, for example, normal exposure is aperture F8 and shutter 1/250. If it is-1EV, it can be set to the aperture F 1 1, and the shutter is unchanged, or the aperture is unchanged and the shutter is 1/500. If it is +2EV, it can be set to the aperture F4, with the shutter unchanged, or with the aperture unchanged, shutter 1/60, or aperture F5.6, shutter1125, and so on.