The correct option is C Each trouble can prove to be a stepping stone
Option B: As it's mentioned in the passage, "But each trouble can be a stepping stone.", this line is the moral of the given passage. It means that every trouble that comes your way, can be used as a means to achieve something greater. Hence option B is correct.
Option A: This line is also mentioned in the passage, "Life is going to shovel dirt on you", but it is not the real moral here.
A moral is a 'lesson that can be derived from a story or experience'.
The line in A states a fact, it does not present the lesson itself. Hence A is incorrect.
Option C: These words have differed in meaning from the original line: "We can get out of the deepest wells by not giving up."
It does not mean that one must fall into a well to succeed in life.
Hence C is incorrect.
Option D is incorrect because the answer lies in B.