A、In Africa. B、In Chicago. C、In Washington. D、In California. D该题询问地点，而整个短文中只出现了California，因此正确选项为D．In California。

Exercise is beneficial to your heart. A 22 - year study was conducted by doctors in California. They found that people who work at physical jobs experience fewer heart attacks than other people. The active people work all the time at moderated speeds. Their daily rountine gives them an adequate amount of exercise and helps them stay in shape. However, machines that can do heavy labor more speedily are replacing this type of work.