When constructing an ellipse, the length of the string used is?

When constructing an ellipse using the string method, the total length of the string is directly related to the dimensions of the ellipse, specifically the semi-major axis. The semi-major axis is defined as the longest radius of the ellipse, while the major axis itself is the full width of the ellipse measured from one end to the other.

In the string method, two foci of the ellipse are established, and the string is fixed at these two points. The characteristic of an ellipse is that for any point on its boundary, the sum of the distances from this point to the two foci is constant. This constant distance corresponds to the length of the string used.

The effective length of the string, being the constant total distance that specifies the relationship with the foci, is equal to twice the semi-major axis. Therefore, the correct answer reflects this fundamental relationship in ellipse construction, affirming that the length of the string must be equal to two times the semi-major axis to accurately create an ellipse.