5. In 2016, the International Union for Conservation
of Nature (IUCN) raised the IUCN Red List threat
level for the giant panda from "endangered" to
"vulnerable." Which of these statements seems the
most reasonable explanation for the upgrade?

A. With new information from satellites and other sources, panda populations seem to be larger than originally estimated
B. Food sources for pandas decreased due to overpopulation.
C. Panda birthrates decreased.
D. Pandas began to immigrate from other areas.​