Do all animals share a common ancestor?

The most recent common ancestor of all currently living organisms is the last universal ancestor, which lived about 3.9 billion years ago. ... 6,331 groups of genes common to all living animals have been identified; these may have arisen from a single common ancestor that lived 650 million years ago in the Precambrian.

the answer is c.) there is a warm front in region a and a stationary front in region b.

only about ten percent of the energy at one trophic level is passed on to organisms at the next trophic level. the remainder of the energy is used in life processes or lost as heat.