The pupil is the opening that allows light to enter the eye. Small mus change i diameter i response t illumination s less li enters un bright condi and mo enters wh surroundings become darker. This adjustment occurs without a conscious decision. After walking from a dim corridor into sunshine, a person does not have to remember to make the opening smaller. Pupil size is only one part of visual adaptation, however. Other processes within the eye also contribute to the gradual improvement in vision when someone enters a dark room.

Type only the missing letters. Each box is one letter, and the number of boxes matches the letters that are missing.