(the skyscraper that was built last year) has the most extraordinary architecture

the parenthesized subject of the sentence is *pick one of the four*
a. an adverbial phrase
b. a noun phrase
c. a prepositional phrase
d. a verb phrase

The parenthesized subject of the sentence the skyscraper that was built last year is B. a noun phrase.
When determining the type of phrase, you just need to locate the center of the phrase. Here, as you can see, the center, or the most important part of the phrase is the noun the skyscraper, which is why this is a noun phrase. 

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.