The spatial datatype used to store a curve is . . . . . . . .

GEOMETRY: The GEOMETRY data type in MySQL is a generic type that can store various types of geometric data, including points, curves, or polygons. However, if we want to specifically store a curve, we use a more specialized type.
POINT: The POINT data type in MySQL is used to represent a single point in a two-dimensional coordinate system. It is not suitable for storing curves.
LINESTRING: The LINESTRING data type in MySQL is used to represent a sequence of points that form a line or curve. It is precisely designed for storing curves.
POLYGON: The POLYGON data type in MySQL is used to represent a closed shape consisting of a sequence of connected straight lines. It is not specifically designed for storing curves.

Therefore, the spatial data type used to store a curve in MySQL is Option C: LINESTRING.