* Adenine (A)

* Guanine (G)

* Cytosine (C)

* Thymine (T)

They pair up in a specific way, forming complementary base pairs:

* Adenine (A) always pairs with Thymine (T)

* Guanine (G) always pairs with Cytosine (C)

This specific pairing is due to the chemical structure of the bases, allowing them to form hydrogen bonds with each other. This pairing is crucial for DNA's function as it ensures that the two strands of the double helix are complementary and can be used as templates for replication.