Some people are living very long lives. What are some of their secrets to longevity?     1    (eat) the right food plays a big role. Exercise is also important. A study found that people who exercised at     2    (recommend) levels gained 3-4 years of life compared to those     3     were inactive. In addition, there is also a link between happiness and lifespan — happy people with a positive outlook on life tend to live     4    (long) and experience better health than their unhappy peers.

Yuan Longping realised that larger fields were not the solution. Instead, farmers needed to boost yields in the fields they had. How this could be done was a     1     (challenge) question at the time. Yuan was convinced that the answer could be found in the creation of hybrid rice. One characteristic of hybrids is     2     they usually attain a higher yield than conventional crops. However,     3     it was possible to develop a hybrid of self-pollinating plants such as rice was a matter of great debate.