Which of the following is true about photoreceptors?

a. if all cones are stimulated equally, all colors are absorbed by the cones and the color perceived is black.
b. rods absorb light throughout the visual spectrum but confer only gray tone vision.
c. in dim light, images are focused directly on the rods in the fovea centralis.
d. three types of color-sensitive photoreceptors exist: red, green, and yellow.

Suppose water is leaking from a tank through a circular hole of area ah at its bottom. when water leaks through a hole, friction and contraction of the stream near the hole reduce the volume of water leaving the tank per second to cah 2gh , where c (0 < c < 1) is an empirical constant. a tank in the form of a right-circular cone standing on end, vertex down, is leaking water through a circular hole in its bottom. (assume the removed apex of the cone is of negligible height and volume.) (a) suppose the tank is 20 feet high and has radius 8 feet and the circular hole has radius 2 inches. the differential equation governing the height h in feet of water leaking from a tank after t seconds is dh dt = − 5 6h3/2 . if the height of the water is initially 8 feet, how long will it take the tank to empty? (round your answer to two decimal places.)