The correct answer is: A. SparseSeries
A SparseSeries is a data structure that stores only the non-zero values of a Series. It is not an indexed object because it does not have a unique identifier for each row or column.
A SparseDataFrame is a data structure that stores only the non-zero values of a DataFrame. It is an indexed object because it has a unique identifier for each row and column.
A SparsePanel is a data structure that stores only the non-zero values of a Panel. It is an indexed object because it has a unique identifier for each row, column, and time period.
In conclusion, A. SparseSeries is not an indexed object.