Why did the Spanish build Elena (town/San Felipe (fort)?

A(n) is a molecule influences the way that a molecule reacts.

What gases are carried by the blood

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.