The correct answer is C. Curved length and the straight distance.
Meander is a bend in a river or stream. The sinuosity of a meander is the ratio of the curved length of the meander to the straight-line distance between its ends. It is a measure of how winding the meander is. A sinuosity of 1 indicates a straight river, while a sinuosity of infinity indicates a perfectly circular meander.
Option A is incorrect because the width of the meander is not relevant to its sinuosity. The sinuosity is a measure of the overall shape of the meander, not its width.
Option B is incorrect because the half width of the river is also not relevant to its sinuosity. The sinuosity is a measure of the overall shape of the meander, not its width.
Option D is incorrect because it is not one of the possible answers.