1. **Problem:** What ratio corresponds to the sine function of an acute angle in a right triangle? 2. **Formula:** The sine of an acute angle $\theta$ in a right triangle is defined as the ratio of the length of the side opposite the angle to the length of the hypotenuse. $$\sin(\theta) = \frac{\text{opposite}}{\text{hypotenuse}}$$ 3. **Explanation:** This means to find the sine of an angle, you divide the length of the side opposite the angle by the length of the hypotenuse. 4. **Answer:** The correct ratio is the ratio of the opposite side to the hypotenuse side, which corresponds to choice C. **Final answer: C. The ratio of the opposite and the hypotenuse sides**