A)O₂ moves slowly through larger cells, so higher concentrations of O₂ had to become available before eukaryotic cells could be efficiently supported.
B)The ability to use O₂ had to evolve before cells could survive in an O₂-rich atmosphere.
C)The ability to break down the waste products of O₂ use had to evolve before cells could use it to create energy.
D)Enough prokaryotes had to become extinct to provide eukaryotes with a niche to occupy before they could evolve.

A)Transitional forms of organisms do not exist because evolution constantly forms new organisms from scratch.
B)The remains of organisms form fossils by chance and are later discovered by chance.
C)DNA evidence cannot be obtained from fossils.
D)Evolutionary trends cannot be determined without complete skeletons, which are rare.

A)Point A
B)Point B
C)Point C
D)Point D