Which sentence uses a contraction incorrectly? O How's your new business venture going?
O There's a guest coming over this afternoon.
O We'd never do anything to hinder your progress.
I think you're graduation is a big achgmplishment.

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.