Large hydroelectric dams: a. have one of the highest (if not the highest) eroei of any energy source. b. produce no co2 emissions to generate the electricity because nothing is burned. c. do little if any environmental damage. d. a and b. e. a, b, and c.

ANSWER IS D

Large hydroelectric dams has been shown to have one of the highest (if not the highest) EROEI (The energy return on investment) of any energy source. Also, nothing is burned when large hydroelectric dams generate electricity, so they do not produce CO2 emissions. However, by altering  a river's flow and, and by their downstream sediment transport, they often cause great sustained environmental impacts.

desert perennials often survive by remaining dormant during dry periods of the year, then springing to life when water becomes available. most annual desert plants germinate only after heavy seasonal rain, then complete their reproductive cycle very quickly.