The correct option is
D Learnt
A synonym is a word or a phrase that is similar in meaning to another word/phrase.
The word 'mastered' means 'acquired complete knowledge or skill in'.
Option B: 'Learnt' means 'gained or acquired knowledge or skill (in something) by study or experience, or being taught'.
So, you can see that 'learn' means the same as 'mastered'.
Hence option B is correct.
Option A: 'Tried' means 'make an attempt or effort to do something'.
Option C: 'Taught' means 'impart knowledge or instruct (someone) how to do something'.
Option D: 'Created' means 'to bring into existence'.
These words do not mean the same as 'mastered'. Hence, options A, C and D are wrong.