Correct answer: C. The number of kinematic equations you will use will depend upon how many missing variables you need to solve for. In regular one dimensional kinematics you often need to solve for only ONE variable, thus need ONE kinematic equation. In two dimensional motion you often need to solve for 2 variables, thus need two equations. This is why answers A and B are incorrect. When you have two or more equations it is also possible to set up a system of equations.
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