Answer: a. anticline
An anticline is a folded rock that bends upwards into an arch. The anticline rock is formed by initially flat rock that attains convex shape from upwards attaining an arch shape. In the process of formation of anticline rock, the older rocks gets deposited in the core region of the rock. Anticline rock formation is indicative of oil reservoir underneath. It is a source of natural gas, hydrocarbon oil like petroleum.