The passage given below is followed by four alternate summaries. Choose the option that best captures the essence of the passage.
A mountain range is easy to think of as something that happened once and then stopped. It is still happening. The rock beneath is being pushed up by a few millimetres a year, about the rate at which a fingernail grows, and rain and frost are taking the top off at a rate not far different. What you see is the difference between two slow processes, not the leftovers of an old event. When the pushing stops, the taking off does not, and the range is worn flat in a span of time that is long by our measure and short by the earth's.
- A
A mountain range is the running difference between uplift and erosion rather than the remains of a past event, so it wears flat once uplift stops and only the erosion goes on.
- B
A mountain range is what remains of a single episode of uplift that finished long ago, and the rain and frost working on it now take almost nothing off its height in a year.
- C
The rock under a mountain range is pushed upward by a few millimetres each year, roughly the rate at which a fingernail grows, while rain and frost remove the top at a similar rate.
- D
Any landscape anywhere should always be described by its rates rather than by its history, because no account of a past event can ever explain the shape of the ground seen today.