This fossil trilobite and this living blue crab both have a limb structure called a biramous limb. What best explains why both species have biramous limbs? A. It is impossible to say. Fossils are very old, so we cannot make observations of the trilobite's ancestors, and we cannot explain its body structures. B. The trilobite and blue crab both share the same ancestor population that had a biramous limb. They inherited this structure from the ancestor population. C. All species have their own specific body structures, so it is a coincidence that this trilobite and blue crab each happen to have the biramous limb structure. D. The trilobite and blue crab are different species, so they must not share an ancestor population. They inherited their biramous limb structure from separate ancestor populations. HELP