The major focus of nutritional recommendations in this century has shifted to:

The correct answer is A: prevention and control of chronic diseases. In this century, nutritional recommendations have increasingly emphasized the importance of preventing and managing chronic diseases like obesity, diabetes, cardiovascular diseases, and cancer. Lifestyle factors such as diet play a significant role in the development of these conditions. Option B, improved sanitation and public health, although important for overall health, is not the primary focus of nutritional recommendations. Option C, prevention and control of infectious diseases, is also crucial but does not reflect the current major focus of nutritional recommendations. Option D, development of healthful foods using food technology, is a valid area of interest but is not the primary shift in focus observed in nutritional recommendations.