I would say it's A because it sounds like the most important one.
Biomes are very large ecological areas on earths surface with plants and animals adapting to that environment.
Examples are desert, aquatic, forest, grassland, and tundra. I hope that helps ☺
DNA is forms a double helix shape/strand. The rule of base pairing is pretty much something that you just need to know by heart. A (adenine), T (Thymine), G (Guanine), and C (Cytosine) and the 4 bases that make up DNA.
***** The most important part is to know that A always pairs with T and G always pairs with C *****
So, the double helix strand of DNA is made up of two strands - kind of like a ladder - one strand is the original, while the other is a replicate of the original strand that is formed through different steps of polymerase reaction etc.
So, for example, let's say strand 1 has this code: ATGCTAGCTGATCG (I made this up, probably doesn't code for anything). But, knowing this, what will it's replicate of second strand look like?
Original strand: ATGCTAGCTGATCG
Replicate Strand: TACGATCGACTAGC
So, you can see from the above example that to form the replicate strand, you just insert the base that pairs with the one from the original strand. A-T and G-C!
Hope that helped!
The sun provides a handy benchmark for describing other stars. The mass of this solar system's sun gives us a unit for measuring other stars' masses. Similarly, the sun's luminosity and surface temperature define the center of the Hertzsprung-Russell Diagram (H-R Diagram). Plotting a star on this chart reliably predicts other qualities of the star, such as mass and age. The main sequence phase of a star's life cycle is that time during which hydrogen fusion takes place in its core. But in terms of the H-R Diagram, "main sequence" also refers to a roughly diagonal, slightly S-curved line stretching between the upper-left and lower-right corners on which main sequence stars chart. They maintain a predictable relationship between luminosity and temperature: the brighter, the hotter. Both of these traits increase with a star's mass; a star indicated closer to the upper-left corner will be "heavier" than our sun, while lower-right main sequence stars will be "lighter."
Red Giants
Should astronomers plot a newly discovered star in the upper-right corner of the H-R Diagram, being both bright yet cool, they'll immediately know what phase of its life cycle the star is enduring. A red giant's core, hot enough to fuse helium and even heavier elements, has pushed its shell layers so far out that they can cool into the red spectrum. They owe their great luminosity not to their temperature, but to their size: bigger stars radiate more light energy.