For what purpose might a playwright include stage directions

Read this paragraph from a cause-and-effect essay. upwelling and el niño in normal years, the trade winds cause colder, nutrient-rich waters to rise to the ocean surface. this process is called “upwelling,” and it causes small fish called plankton to multiply. which rubric term or phrase would apply to the phrase “trade winds”? a. effect b. elaboration of a cause or effect c. transition between a cause and an effect d. cause