Which type of sentence is the sentence below?

to train a knight, a boy became a squire at about age fifteen; a squire assisted a knight and learned more about fighting.

simple

compound

complex

compound-complex

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.