Which is the priority to control exposure? Shutter or aperture or ISO?

First of all, the "XX priority" you mentioned is actually an automatic mode. Excellent exposure means that the shutter takes precedence, and you can get used to it with the aperture when the shutter is unchanged. Simply put, first set the aperture, fix the aperture, and let the camera automatically use the shutter to adapt, thus controlling the imaging quality. ISO is the sensitivity of film to light. The larger the ISO, the shorter the shutter can be, but at the expense of imaging quality. In the case of sufficient light, the lower the ISO, the better.

I've been thinking about the mountain for a long time, because it doesn't usually happen when shooting. Then it suddenly occurred to me that you must have taken it against the light, and it was dark. This is the objective law of backlight, and many photographers take this kind of photos specially, which is called silhouette effect. If you must change, you must flash or change your angle.