# The substance not likely to contain CaCO3 is

$(a)\;\text{calcined gypsum} \\(b)\;\text{sea shells} \\(c)\;\text{dolomite} \\ (d)\;\text{a marble statue}$

Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula $CaSO_4. 2H_2O$
Hence a is the correct answer.