The bases in DNA pair by chemical interactions. How are the base pairs formed differently between the pairs? A. Adenine and thymine form two hydrogen bonds, while cytosine and guanine form three hydrogen bonds.
B. Adenine and thymine form three hydrogen bonds, while cytosine and guanine form two hydrogen bonds.
C. Adenine and thymine form covalent bonds, while cytosine and guanine form hydrogen bonds.
D. Adenine and thymine form hydrogen bonds, while cytosine and guanine form covalent bonds.

Explanation:

The two strands are held together by hydrogen bonds between the bases, with adenine forming a base pair with thymine, and cytosine forming a base pair with guanine.

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

explanation:

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