Direction: Read the following paragraph and fill in the blank with the number. Paragraph Two: 1. My grandfather contracted lung cancer a few months ago. 2. The doctors now say that he only has a few weeks to live. 3.My family’s situation is not unique. 4. Millions of Americans are going through a similar experience. 5. At least three members of every extended family will contract a terminal disease before the age of sixty. 6. At least one out of every three nuclear families will have a member who will die of cancer before the age of fifty. 7. From these statistics and from personal experience it is evident that no one is unaffected by cancer. The topic sentence of the paragraph is_________(写上面段落中的序号即可)