In a paper on photosynthesis in a desert cactus, in which section would you find a review of existing knowledge that is relevant to the experiment ?

A. Conclusion

B. Materials and Methods

C. Results

D. Introduction

The gene that causes sickle-cell disease is present in a higher percentage of residents of sub-saharan africa than among those of african descent living in the united states. even though this gene causes sickle-cell disease, it also provides some protection from malaria, a serious disease that is widespread in sub-saharan africa but absent in the united states. discuss an evolutionary process that could account for the different percentages of the sickle-cell gene among residents of the two regions.

9. wind power creates pollution. water air soil noise

What environmental cues and landmarks do the geese use to determine the timing and direction of their migration over the mountains? how do they find their way?