The correct option is B advanced
The word 'elementary' refers to something of the most basic kind.
Option A, secondary refers to something subordinate or lesser importance.
Option B, tough refers to becoming strong and durable.
Option C, advanced refers to going far on or ahead in progress or development.
Option D, simple refers to being easily understood or done.
Thus, according to the meaning, the word 'advanced' is the opposite of the word 'elementary'.