Which of the following sentences contains a plural spelling error? She had to use crutchs for several weeks after breaking her leg.
He was used to practicing on many different types of pianos.
The cashier collected the monies and deposited them.
We all tried to find the keys but had no luck at all.

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.