What are the three characteristics of all vertebrates

Which of these is not a nucleotide base found in dna?

What is a general feature of a species that varies from one individual to the next (skin tone,eye color or hair color)? a.organism b.trait c.character

Ruby is conducting an investigation. an advantage of her design is that she can use a large range of variables, with that she can not be sure that one variable is the cause of another. what kind of investigation is ruby most likely conducting?