In question 4, you estimated the time for lowering the surface of happy valley enough to account for the modern difference in elevation between the top of mount nittany and the bottom of thevalley. in question 5, you saw that you could change that estimate a good bit. but, to make a 10-fold change in the estimate, you had to assume things that are really almost impossible, such as making central pennsylvania one of the wettest places on earth. we could tweak the assumptions in the calculation to move the estimate either way by a few-fold (so 10 million years could become 3 million years, or 30 million years, without too much trouble), but shifting the answer a whole lot further than that requires impossibilities or miracles--just becausewe can shift it to 3 million years or even 1 million years does not mean we can shift it to 10,000 years, which would require diggingthe valley 1,000 times faster than is happening now, which nature really cannot do here. we can say something else important, though. whatever the timeneeded for deepening the valley, the geologic story of central pennsylvania must be much longer than that--time-deepening thevalley is only the last act of a long play. the text of this exercise refers to several reasons why we know that the story is longer than the deepening of the valley. which statement below describes something indicating that the region is much older thancalculated so far in this exercise? two of the five answers are correct; pick one of the correct ones for full credit. a) mountains are always old. b) the mountain top is being eroded as well as the valley, so more rock must have been removed from the valley than you calculated to give the modern difference in elevation between mountain top and valley. c) "clams got legs", clams keep jogging to central pennsylvania from the chesapeake bay and then dying, the stream has to carrythe clams away, so that means that the time to dig the valley was more than 10 million years. d) the rocks needed to be formed before they could be eroded, and forming rocks takes time, too. e) just because.