Hydroelectric power produces electricity using a. tidal movement b. pressurized c. falling water d. geothermal

The prefix Hydro is a 19th-century-word meaning water. 
You can automatically rule out both B and D. While pressure DOES have to do with water, the energy doesn't come from the pressure, but the movement itself.

Now, this doesn't mean A is correct. Tidal power has a similar use, but still not quite the same.
However, hydroelectricity is produced using a special setup involving "Falling Water", which creates energy. 

Your answer is C: Falling Water

~Hope this helps!