Final answer:
In DNA structure, Thymine (T) always pairs with Adenine (A) as per Chargaff's rule. Other pairings mentioned are not the normal base pairings in DNA.
Step-by-step explanation:
Among the options given, the base pairing that normally occurs between two strands of DNA is Thymine (T) to Adenine (A). In DNA, the rule of base pairing or Chargaff's rule dictates that Adenine always pairs with Thymine and Cytosine pairs with Guanine. This specific pairing is crucial for DNA replication and transcription into RNA. The other base pairings mentioned (A to C, G to T, and C to T) are not the standard base pairings in the structure of DNA. In DNA, the bases adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G). This is known as complementary base pairing.
The other options are incorrect:
A to C: Adenine pairs with thymine, not cytosine.
G to T: Guanine pairs with cytosine, not thymine.
C to T: Cytosine pairs with guanine, not thymine.
Learn more about DNA base pairing