The two most common types of folds are

These are anticlines the synclines folds.

Explanation:

The anticline is those folds where half of the fold dips away form the crust and the synclines are those folds where half of the folds bends to the trough of the fold. Being an arch-shaped fold is convex with the hinges or crust turns to the location. The progressive age of the rock strata to the core forms the uplifted centers and that indicates the nature of the anticline and this develops around a thrust fault.  While the syncline is a fold where the youngest rocks occur in the core of a fold. And the features of the syncline is that of a concave and is separated by the axial plains.

A,b,c is the answer to the question