Suppose some female rats are given caffeine and others are not. the researchers then count how many times the rats given caffeine couple with males and how many times the rats not given caffeine couple. in this example the independent variable is

c.) polymerase chain reaction

- "unlike the original dna fingerprinting method, dna profiling does not use restriction enzymes to cut the dna. instead it uses the polymerase chain reaction (pcr)? to produce many copies of specific str sequences. pcr is an automated procedure that generates lots of copies of a specific sequence of dna."

the dark variety, as they are not visible on the dark tree barks

explanation: