C. A heavy rainstorm.
The text shows indication of a storm arriving. “Clouds arrived” are an indicator that clouds quickly appeared. “Lightning flashed” tells us these are storm clouds. It makes sense that next it would start raining, making the next event a heavy rainstorm.
C) "This data is totally useless and doesn't help us at all in solving the problem."
As per assembling a writing plan for an essay, the better answer, if not the best, would be B. Material that catches the reader's interest.
Many would argue that the correct answer would be D. the general idea of your essay or maybe C. a brief summary of your conclusion or perhaps A. the first section of the body of your essay. Well, they are all correct. As long as what follows is duly taken noted and is consistent to keep the flow of the essay that when the final paper is read, it isn't confusing in any way. Though generally speaking, what should come first would be the material that catches the reader's interest.