题目选项分析

There are many theories as to why people develop cancer, but none explain why so many of the people who practice healthy habits do develop cancer and, conversely, why such a large number of people who practice unhealthy habits have not.

There are many theories as to why people develop cancer, but none explain why so many of the people who practice healthy habits do develop cancer and, conversely, why such a large number of people who practice unhealthy habits have not.