Cells contain a cell wall that is not found in cells.
a. animal, human
c. plant, animal
b. human, plant
d. animal, plant

How can a geological time scale best be reconstructed? a) comparing vestigial structures in living species b) comparing homologous structures in living species c) examining homologous structures in fossil remains d) examining the written records of scientists from past cultures

What is used to keep track of the gamates and possible offsprings combination

Which of the following is a reason why early living organisms on earth could not have survived on the surface? 1. the lack of an ozone layer 2. the lack of oxygen in the atmosphere 3. the fact that these organisms were single-celled