NIKOND90 SLR shoots "indoor portrait prospect", but it is always either all white or all dark?

This is the tolerance of exposure. Two objects with very different amounts of light cannot be perfectly compatible in photosensitive materials. There are three ways, 1, to fill light for dark things, such as reflectors or flashlights; 2, HDR, which needs to be completed later or in the camera HDR mode. 3, two exposures, measuring people and scenery respectively, taking two photos, and later synthesizing.