To what depth below earth's surface do you have to go before the pressure and temperature cause rocks to melt?
a. at depths of about 500 to 1000 km below earth's surface
b. at the boundary between earth's mantle and core
c. at depths of about 50 to 200 km below earth's surface
d. at any point below earth's crust

Option C, At depths of about 50 to 200 km below Earth's surface

Explanation:

The molten rocks with in the earth is found in the mantle layer. The upper mantle layer starts from 100 kilo meters to 200 hundred kilometers below the earth crust. The temperature and pressure at such depths is extremely high due to which the rocks starts melting. Even if the temperature is low , the excessive pressure leads to liquification of rocks.  

Thus, option C is correct as  from this depth onward the melting of rocks starts.

what are the options