What is a selective breeding technique used to breed purebred racehorses?

Which of the following must be true for a fossil organism to be useful as an index fossil? a. the fossil organism must be widespread geographically. b. the fossil organism must be abundant. c. the fossil organism must be limited to a short span of geologic time. d. all of the above.

Define adaptation. why do organisms adapt? give an example.

Besides regulating what enters and leaves the cell, what is another function of your choice from question #1?