Why The piezoelectric effect is a two-way coupling between mechanical stress and electric charge in certain crystals such as quartz, Rochelle salt and various ceramics. Squeezing or bending the crystal produces a voltage across it, and conversely applying a voltage makes the crystal physically deform or vibrate. That reciprocal behavior is what lets a quartz crystal act as a very high-Q mechanical resonator in oscillators and filters, and what drives ultrasonic transducers and buzzers.
Watch out Deformation caused by a magnetic field is magnetostriction, a different effect (it is what makes transformer cores hum). The light-related choices describe photovoltaic action and photoconductivity.
Piezo = pressure and electricity, no magnets and no light. Squeeze it for volts, apply volts and it squirms.