Instead of submitting a copy of your teaching certificate with your application, you may submit verification that you are matriculated in a certification program (e.g., letter of acceptance, letter from advisor).
Expository writing is writing that seeks to explain, illuminate or 'expose' (which is where the word 'expository' comes from). This type of writing can include essays, newspaper and magazine articles, instruction manuals, textbooks, encyclopedia articles and other forms of writing, so long as they seek to explain.
This article describes the writing process of an expository essay with a focus on some general types of expository essays. A point that I want to articulate is that each paragraph in your expository essay should have its idea. This would allow your essay to be clear and have minimal repetition.