The correct answer is (b). Concave mirrors are used to focus light, not to search for it. They are used in searchlights, headlights, and telescopes to collect and focus light. They are also used in solar cookers to focus sunlight on a small area to cook food.
(a) Mirage is an optical illusion that can be seen in hot, dry areas. It is caused by the refraction of light as it passes through layers of air with different temperatures. The hot air near the ground is less dense than the cooler air above it, so light bends as it passes from the hot air to the cooler air. This can cause objects to appear to be floating in the air or to be located in a different place than they actually are.
(c) In summer, white or light-colored clothes are preferred to dark-colored clothes because they reflect more sunlight and absorb less heat. This helps to keep the body cool. Dark-colored clothes absorb more sunlight and heat, which can make the body feel hot.
(d) Convex mirrors with a small aperture are used by doctors to examine the ear, nose, or throat of a patient. The small aperture helps to focus the light on the area being examined.