Fill in the blank with appropriate option.There is nothing interesting in mathematics. I _ read grammar.

Explanation

The correct answer is 'might as well' because it suggests that, given the lack of interest in mathematics, the speaker sees reading grammar as a reasonable alternative. The phrase implies a decision made due to the circumstances, rather than a necessity or ability. The other options - 'could', 'can', and 'must' - do not fit the context of this choice. 'Could' and 'can' imply ability rather than preference, and 'must' implies obligation rather than a casual decision.