Final answer:
W4D underestimates suppression in normal viewing because it lacks monocular depth cues, which are essential for depth perception in day-to-day life.
Step-by-step explanation:
The student has asked why W4D underestimates suppression in normal viewing. The most accurate answer is: A) It lacks monocular depth cues. This is because suppression can occur when binocular disparity is not properly processed or when one eye's input is disregarded by the brain, and W4D primarily considers binocular cues (such as those involved in binocular rivalry) but may not adequately take into account the monocular depth cues that contribute to our perception of depth in day-to-day life. Monocular cues, such as the size of objects or their overlap with one another, provide important normal depth information in isolation and are therefore critical for accurate depth perception even when both eyes.