Correct Option: A

The given sentence states that the speaker did not succeed in all the aspects or fields that he had planned to, five years ago. Option (a) is correct, because ‘set out to’ refers to what was planned or specifically decided, so it fits perfectly into the sentence. Option (b) is incorrect. Options (c) and (d) are incorrect, because ‘thought’ means something that was merely considered or contemplated, it does not mean that it was planned or it was the final decision. Also, ‘thought to’ is a wrong usage of the preposition: ‘to’.
As we can say that ,
The correct word is filled in the above given sentence :-
I am always the first to admit that I have not accomplished everything that I set out to achieve five years ago.