What structure do angiosperms have and gymnosperms lack?

Give examples of selective advantage of organism’s body part/organ

Why are common names a problem for scientist?

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.