Two Observed Features on Mars Appear to Lead to Contrary

Multiple Choice

Two observed features on Mars appear to lead to contrary geological conclusions-the appearance of massive, solitary volcanoes, apparently caused by hot spots under the planet's surface, and the discovery of a long, deep rift valley across the planet. Why are the two features a contradiction?

A) Volcanoes suggest a molten inner planet, whereas a rift valley suggests the presence of a solid core.
B) Massive volcanoes should have covered the planet's surface, including the valley, with dust and ash, but the valley remains as a major feature.
C) Ancient volcanoes show no sign of erosion by water, whereas the valley suggests prolonged rainfall and erosion.
D) Single massive volcanoes indicate hot-spot volcanism with no plate tectonic motion, whereas a rift valley suggests otherwise.