Two sounds the speaker describes in “stopping by woods on a snowy evening” are —
choose one answer.
a. his own voice and his horse’s neighing
b. wind howling in the bare branches and sleigh bells
c. his own voice and the voice of the owner of the woods
d. harness bells on a horse and wind during a snowfall

The correct answer is D, because at some point the horse shakes his harness bells, and then the author says 'the only other sound's the sweep of easy wind and downy flake'. The protagonist is not speaking anything, so A and C cannot be correct. And no sleigh bells are ever mentioned in the poem. 

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.