Which statement is true about the turbine in a hydroelectric dam? a. it is turned by wind and provides a direct current. b. it is turned by water to produce a direct current. c. it is turned by water to turn a wire inside a magnet. d. it is turned by wind and provides an alternating current.

Option C,  It is turned by water to turn a wire inside a magnet.

Explanation:

In a hydroelectric power plant, the water is stored and then releases from greater heights which produce force enough to turn the turbine. These turbine then activates a generator to produce electricity. With in the generator a wire is set between two magnets , which start rotating to produce AC current.  

Electricity produced by rotating wire fixed between the magnets is always an AC current. Therefore option B is incorrect.  

Option A and D is incorrect as in producing hydroelectric energy it is the water which is used to rotate the turbine and not the wind. Also only AC current is produced by the hydroelectric dam.