What is the meaning of the word "catalyst" as it is used in the following sentence? tragedies are often a catalyst that causes communities to come together.

a a common enemy
b a complex chemical reaction
c something that causes a change
d an event that makes people sad

An expository essay instructs, provides information, or explains. in this essay, you are presenting information and explaining why you think the ideas and work of the individual you chose had an effect on european thought. but before you begin writing the essay, you need to organize the information you’ve gathered by creating an outline. directions: your taking notes sheet should have you identify and organize the information you found while doing your research. now it is time to create an outline to organize the information in the way you will present it in your essay. you may decide not to use all the information you gathered, but be sure you do not leave out anything that you believe is important to support your thesis. your essay should include an introductory paragraph, supporting paragraphs, and a concluding paragraph. each paragraph should cover one main topic and should correspond to a roman numeral (i., ii., iii.) on the outline. the main topics should cover: the person’s accomplishment and contributions, and the effect of his or her accomplishments or contributions on european thought. write a topic sentence for each paragraph of your essay. be sure it tells the reader what the section will be about and how the information relates to your thesis statement. your topic sentence for the introductory paragraph might say something like “johannes gutenberg’s invention changed the way people communicated.” a topic sentence for the second paragraph—the first main topic—might be something like "gutenberg’s printing press changed the way books were produced and the way knowledge was communicated.” decide which pieces of information you will use to support your topic sentences. (these ideas or groups of facts are called subtopics.) subtopics follow capital letters and periods (a., b., and c.) on your outline. add this information beneath your topic sentence. you can further divide subtopics into specific facts. in an outline, specific facts follow arabic numerals and periods (1. 2. 3. 4.) end your outline and essay with a concluding paragraph. write a concluding paragraph that summarizes the main ideas of your essay and restates your thesis statement in some way. write no more than four or five sentences. worth 241 points