Concept:Oil and natural gas collect in folded rocks when an upfold or anticline traps them beneath an impermeable cap rock.
Explanation:Folding bends rock layers into upfolds called anticlines and downfolds called synclines.
Oil and natural gas are lighter than water, so they rise through porous rock layers.
In an anticline, the crest forms a natural trap, and the impermeable cap rock prevents the oil and gas from escaping.
This is why gas collects above oil in the anticline.
A syncline is a downfold, while horst, cuesta, and nappe are different structural or erosional features and are not the usual petroleum traps.
Therefore, the required feature is an anticline, but anticline is not present among the options.
Answer:Oil and natural gas usually collect in an anticline. Since anticline is not listed among the options, none of A–D is correct.