Here's why:

* DNA is a double helix: This means it consists of two strands that are intertwined.

* Each strand is made of nucleotides: Nucleotides are the building blocks of DNA, and each nucleotide has a sugar, a phosphate group, and a nitrogenous base.

* The bases pair up: The two strands are held together by hydrogen bonds between the nitrogenous bases. Adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G).

So, while each strand has a sequence of bases, the double helix itself is made of two sets of bases that are paired together.