What part of the digestive system first causes chemical changes to food? A. teeth in the mouth
B. saliva in the mouth
C. enzymes in the stomach
D. enzymes in the small intestine

Which of the following is one of the four conditions necessary for natural selection to occur in a population? fewer organisms are born than the habitat can support mutation does not occur organisms have identical characteristics variation is inherited

How does the molecular clock work? a. it analyzes the brain functionality of two different species. b. it examines and compares the physical characteristics of two different species. c. it illustrates relationships between two different species. d. it compares the number of mutations that exist in the dna of two different species.

Nasa scientists must work together to make sure that everything is correct and accounted for when launching a shuttle. besides a physicist, what other type of scientist would be in making sure that the shuttle has the appropriate type and amount of fuel to reach its destination?