Base pairing recall — In standard double-stranded DNA, adenine (A) consistently forms base pairs with which partner base?

Introduction / Context:
Base pairing ensures faithful storage and copying of genetic information. Knowing the A–T and G–C rules is fundamental for interpreting replication, mutation effects, and primer design in PCR and sequencing workflows.

Given Data / Assumptions:

• We consider DNA, not RNA (where uracil replaces thymine).
• Standard Watson–Crick pairing is assumed.
• No modified bases or special pairing modes are considered.

Concept / Approach:
In DNA, adenine pairs with thymine via two hydrogen bonds; guanine pairs with cytosine via three. These specific interactions contribute to the uniform width of the double helix and underpin sequence-specific recognition by proteins. Therefore, adenine’s correct partner in DNA is thymine.

Step-by-Step Solution:

Verification / Alternative check:
Melting temperature correlations with GC content implicitly confirm the different bond counts (A–T two, G–C three) while preserving A–T pairing specificity.

Why Other Options Are Wrong:

• Guanine/Cytosine: pair with each other, not adenine.
• None: incorrect because thymine is correct in DNA.

Common Pitfalls:
Transferring RNA rules to DNA; remember, A pairs with T in DNA and with U in RNA.

Final Answer:
Thymine