The right answer is D. anticlines and synclines.
In geology, we call anticline, a convex fold whose center is occupied by the oldest geological layers.
This means that the term "anticline" takes into consideration a stratigraphic and therefore chronological notion, and thus refers to a specific episode of folding.
In simple cases, an anticline is an antiform at the heart of which are the oldest layers; but if the fold is spilled, the youngest layers can appear in the heart of a synform: it is a "diving head": the earth is raised.
The anticlines are very good hydrocarbon traps.
In geology, a syncline is a fold whose concavity is turned upwards, the anticline having concavity downwards. Under normal conditions, the youngest layers being the upper layers, after erosion, one finds the most recent geological strata in the heart of the syncline. This criterion makes it possible to highlight the succession of synclines and anticlines on a geological map. There are anticlines and synclines at different scales of observations, from microplots, affecting a sample, to regional folds, visible only in cartography. The synforms are structures of equivalent forms but whose stratigraphic logic is unknown or even reversed.