The purpose of the following scene is (A) to show that all men are mortal and therefore Ivan Ilyich, a man, must die.
The syllogism draws a conclusion that since Caius is a man, and men are mortal, they (men, i.e. mortals) must all die.
The answer is:
A. To show that all men are mortal and therefore Ivan Ilyich, a man, must die