What are the stages of intercellular signaling

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

Fossils of ancestors of the modern horses show a small 4-toed almost dog-like browsing animal named eohippus over time the horses got larger lost toes and changed to a grazing diet what is the best explanation of why this change occurred

What are some of the immune functions of the lymphatic system? a. cleaning red blood cells from the blood and creating lymph fluids b. transporting lymph to the tissues and creating lymph fluids c. removing infectious agents and making white blood cells d. making red blood cells and removing infectious agents