This passage is adapted from Allie Wilkinson, “Panda Guts Not Suited to Digesting Bamboo.” ©2015 by Macmillan Publishers Limited.

Scientists suggest that the gut bacteria of giant pandas (Ailuropoda melanoleuca) may not have not evolved to efficiently break down cellulose, a hard-to-digest fiber found in the plant walls of bamboo, as previously thought.

Ancient giant pandas, which were originally omnivorous, began introducing bamboo into their diet at least 7 million years ago, and eventually switched to eating bamboo exclusively 2.4 million to 2 million years ago. The bears evolved strong jaws and a “pseudothumb” to help them to consume the plant. But unlike other herbivores, they did not develop an elongated digestive tract or enzymes to help break down tough plant parts.

Scientists studying the panda gut biome discovered that it is more closely related to that of carnivores, than other herbivores. The scientists found little diversity in the microbes that live in panda guts, and none of the cellulose-degrading bacteria typically seen in other herbivores.

Other scientists argue that some of the microbes in the panda gut might still be highly efficient at breaking down cellulose. They have pointed out that this study only examined microbial composition and not function—and microbes can change function rapidly, making it hard to predict how they perform solely on the basis of the genera of bacteria present.

Question
Which of the following tables accurately reflects the change in pandas’ main energy source over the past seven million years as ancient pandas evolved into modern pandas?