There are 2 variables in the original condition (a and b), and in order to match the number of variables to the number of equations, we need 2 equations. Hence, there is high chance that C is the correct answer. Using the condition 1) and the condition 2), we get (a,b)=(0,5),(-1,6). The answer is unique and the condition is not sufficient. Hence, the correct answer is E.

- Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.

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