The U.S. has more than 87,000 dams greater than six feet high (and two million overall). While many dams continue to provide benefits such as flood control, irrigation, and water supply, for other dams the cost of maintenance or the negative effects on communities, fish, and tribes justifies their removal.
Dam owners and regulators decide whether to remove a dam by weighing many factors including: the cost of removal and the ability to replace any lost power generation against avoided long-term maintenance; safety concerns; benefits to endangered fish populations; increased recreational and commercial fishing; and restoration of cultural values of nearby tribes.
By 2020, roughly 70% of dams will be more than 50 years old, inviting us to reconsider the value to the public of long-term investments in this infrastructure.
Answer:
An eon
Explanation:
The first broad division of the geologic timescale is the eon. Others are Eras, Periods and Epoch.
Eons are the most broad and the largest of divisions of the timescale. There are two categories of the eons which are:
- Hadean eon
- Archean eon
- Proterozoic eon
- Phanerozoic eon
The Phanerozoic eon is the most recent. The Hadean eon is the is the oldest eon.
D. All three
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im prtty sure its A but i dont know but hopefully its right
HOPE DIS HELPS :)
