What are the genotypes of the parents in the monohybrid cross below if the following offspring genotypes are predicted? a) tt and tt b) tt and tt c) tt and tt

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.