The two strands are held together by Hydrogen Bonds
Evolution....................................
Charles Darwin visited the Galapagos islands and found a lot of evidence supporting evolution
The finch species evolved to different habitats on the Galapagos, some had large beaks to crack open large nuts, some had longer, slenderer, and sharper beaks to get at insects (food) in small places like in dead trees
If I remember correctly, it's the Independent variable, since the amount of sunlight (determined by where the plant was placed) controls how much it grows, but I'm not 100% sure. I know for certain that it's not 2 or 3.
There are so many species in the millions of years discovering each one. Classifying is one way that organizes all types of species into categories, knowing what they are, their characteristics, their habitat, etc