Limestone is the parent rock of the nonfoliated metamorphic rock called a. marble b. anthracite c. gneiss d. quartzite

Deeply buried rocks in the ground undergo metamorphism due to high pressure and temperature. Depending on the direction of stress or pressure the rocks have different textures and are either foliated or non-foliated. Non-foliated rocks have different compositions due to different parent metamorphic rocks. The metamorphism of Limestone results in Marble. 

Therefore the correct answer to this question is
Option A. Marble.

Your answer would be 625,000,000.