Which of the following sentences has a Nonessential clause?
A. Every student who passed the test can go to recess.
B. All runners who are eligible for this race line up
here.
C. New reporters, which are actually quite a few,
should report to the registration desk.
D. The swimmer who won the Olympic Gold Medal was
Michael Phelps.

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.