The length of a meander is the distance along the river between the tangent point of one curve to the tangent point of A. Reverse curve B. Next curve of the same order C. Reverse curve plus the width of the river D. None of these

The correct answer is: A. Reverse curve.

A meander is a loop in a river. The length of a meander is the distance along the river between the tangent point of one curve to the tangent point of the reverse curve. The tangent point is the point where the tangent line to the curve meets the curve.

The other options are incorrect because they do not take into account the tangent point of the reverse curve. Option B is incorrect because it only considers the next curve of the same order, not the reverse curve. Option C is incorrect because it adds the width of the river to the length of the meander, which is not necessary. Option D is incorrect because it is not a valid option.