In a gas lighter, mechanical energy is converted into electrical energy by using crystals of barium titanate. Barium titanate is:

Barium titanate is the inorganic compound with the chemical formula BaTiO3. This titanate is a ferroelectric ceramic material, with a photorefractive effect and piezoelectric properties. It is used in capacitors, electromechanical transducers and nonlinear optics. So barium-tintate acts like piezoelectric as well as ferroelectric. Hence option B is correct.