A group of students were collecting soil samples near a river. One student noted there was a lot of sand in one of the samples. He said, “All this sand must have washed up from the beach where the river enters the ocean.” Another student said, “I think it came from the rocks in the mountains. But there aren’t any mountains near us. I don’t understand how the sand got there.”

What would you tell the students to help them solve where the sand came from?
(science)
answer below