Why is the following statement an apt comparison? "ana’s neighborhood is like a cheap hotel—you stay until you’ve got enough money to leave. "

It can be assumed that Ana's neighborhood is not a very good place to live, just as cheap hotels are not often places that someone stays for a long period of time unless they can't afford any of the other options. Once they have enough money they leave as soon as they are able. 

Okay, biology isn't exactly my strongest subject (it never has been), but i'm pretty sure the answer is nucleotides. dna is made up of nucleotides. each nucleotide contains a phosphate group, a sugar group, and a nitrogen base. there are four different nitrogen bases: adenine (a), thymine (t), guanine (g), and cytosine (c). a always pairs with t, and g always pairs with c.