It is important to note, that the 2nd Law of thermodynamics plays no fundamental role in answering this question; we need a heat sink because the entropy is a state function, and at the end of the reversible process (which is visualized through the Carnot cycle diagram relevant for this problem), the entropy value of the system must return to the value it had originally.
a. Rods are about 1000 times more sensitive than cones.
Explanation:
The answer choice shown is a direct copy of the first line of the problem statement. It doesn't appear to be any more complicated than that. (It's a reading comprehension question.)
To find this simply draw a triangle with the hypotenuse being 15 and the angle between the hypotenuse and bottom leg is 20. The horizontal component is the horizontal leg. to find this you would use cos and then solve for the bottom leg.