Either adenine and guanine or thymine and cytosine. It is either because the first adenine pairs with thymine and guanine pairs with cytosine, So each rung will have one of the two pairs.
Answer:
number B i think
Explanation:
The competitive exclusion principle tells us that two species can't have exactly the same niche in a habitat and stably coexist. That's because species with identical niches also have identical needs, which means they would compete for precisely the same resources
upwelling cold sinks, warm rise. suponification