文章首段、中间段以及尾段选项标志词
文章首段选项标志词：
1. Concept, conception, notion, explanation, core, essence, analysis, justification, definition+of+文章标题
2. What is, what makes, what leads to+文章标题
3. Defy, justify+文章标题
文章末段选项标志词：
effect, impact, consequence, result, summary, conclusion+文章标题