Which DNA bond is correct?

a. A-T c. C-A

b. G-T d. C-T

A. A-T

Explanation:

The nitrogenous bonds in DNA bond like so:

Adenine with Thymine, or A with T

Cytosine with Guanine, or C with G

A: A-T

This bond is correct. Adenine is with thymine.

B: G-T

This is incorrect. Guanine (G) should bond with cytosine (C), and thymine (T) with adenine (A).

C: C-A

This is also incorrect. Cytosine (C) should bond with guanine (G), and adenine (A) with thymine (T).

D: C-T

This is incorrect as well. Cytosine (C) should bond with guanine (G), and thymine (T) with adenine (A).

The correct bond is A: A-T, adenine with thymine.