Introduction:
In this question, we are given a polynomial and asked to determine its degree based on the number of points where it intersects the x-axis. We need to explain why the correct answer is option 'C' - cubic polynomial.

Explanation:
A polynomial is an algebraic expression consisting of variables and coefficients. The degree of a polynomial is determined by the highest power of the variable in the expression. Let's consider each option and analyze why only a cubic polynomial can intersect the x-axis at 3 points.

a) Linear Polynomial:
A linear polynomial has a degree of 1 and is in the form of "ax + b". It represents a straight line on the graph. A linear polynomial can intersect the x-axis at most once. Therefore, it cannot satisfy the condition of intersecting the x-axis at 3 points.

b) Quadratic Polynomial:
A quadratic polynomial has a degree of 2 and is in the form of "ax^2 + bx + c". It represents a parabola on the graph. A quadratic polynomial can intersect the x-axis at most twice. Therefore, it also cannot satisfy the condition of intersecting the x-axis at 3 points.

c) Cubic Polynomial:
A cubic polynomial has a degree of 3 and is in the form of "ax^3 + bx^2 + cx + d". It represents a curve on the graph. A cubic polynomial can intersect the x-axis at most three times. Therefore, it satisfies the condition of intersecting the x-axis at 3 points.

d) Biquadratic Polynomial:
A biquadratic polynomial has a degree of 4 and is in the form of "ax^4 + bx^3 + cx^2 + dx + e". It represents a curve on the graph. A biquadratic polynomial can intersect the x-axis at most four times. Therefore, it exceeds the condition of intersecting the x-axis at 3 points.

Conclusion:
Based on the analysis above, it can be concluded that if the graph of a polynomial intersects the x-axis at 3 points, then the polynomial must be a cubic polynomial. Hence, the correct answer is option 'C'.