What statement is best supported by the survivorship curves? a. american robins have a high survival rate for most of their lifespan and then decline rapidly in old age. b. younger american robins have higher death rates than older american robins, while younger and older common green darners have similar death rates. c. a very high proportion of common green darners reach adulthood and live to older ages. d. american robins have similar death rates throughout their lifespan, while the death rate of common green darners changes over their lifespan.