Why does adenine always pair with thymine and guanine with cytosine in dna?

What came first the elephent or the crocodile

One statements is an example of a scientific observation. another statement is an example of a scientific explanation. identify the correct statement for each category to illustrate how scientific explanations are inferred from scientific observations.

What is one way intensive agriculture can contribute to climate change? a. tree loss to agriculture increases earth's albedo b. livestock manure absorbs greenhouse gases c. large herds of livestock release greenhouse gases d. fewer trees are available to replenish petroleum stores appex