The outermost part of the brain, which is made up of tightly packed neurons and is only a tenth of an inch thick, is called the

only b 

There are four nitrogenous bases that make up dna. the two pyramidines are thymine and cytosine. the two purines are adenine and guanine. these bases pair in a very specific way. adenine - thymineguanine - cytosine i remember it like this: a tall, good cat.