Which answer is not a real-life example of geologic cross sections?

road cuts

stream valleys

cliffs

a river

B) Stream valley is NOT a real-life example of geologic cross sections.

Geologic cross-section whether theoretical through drawing or practical in the case of real-life show the intersection of geologic features. The section shows different rocks types, their relationship which represents their geometry, and the internal structures.  All the other mentioned features in options reveal information about rocks and the different layers except for the stream valley.

Stream valleys are the results of erosion which in turn create a depression in the land that carries water flowing at the very lowest point of the basin. It doesn't reveal any information about the geology of the place.