Every 18 months, during the spring tide, the moon is at its closest distance to the earth, called its this produces gravitational forces that are very strong and cause extremely high tides.

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.

What is gene flow? apexa: selection for average traits b: when a population splits in twoc: a mutation becoming more commond: genes moving between two populations

Can someone give me the answers to this?