Select the correct answer from each drop-down menu. The backbone of DNA and RNA is composed of _ groups. DNA is double stranded due to interactions between adenine, cytosine, guanine, and thymine, which are _. Uracil is a _.

Answers:
1. sugar and phosphate groups
2. bases
3. base found in RNA

Which of the following observation darwin shape his concept of descent with modification? a) species diversity declines farther from the equator. b) fewer species live on islands than on the nearest continents. c) birds live on islands located farther from the mainland than the bird's maximum nonstop flight distance. d) south american temperate plants are more similar to the tropical plants of south america than to the temperate plants of europe. e) earthquakes reshape life by causing mass extinctions.