Which of the following foods is naturally a rich source of polyunsaturated fatty acids?Multiple ChoiceWalnut oilGreen beansWhole milkRoast beef

The food that is naturally a rich source of polyunsaturated fatty acids among the options given is Walnut oil.

Here's why:

1. Polyunsaturated fats are essential fats that your body needs for certain functions, such as building cell membranes and covering nerves. They are considered "good" fats and can help improve blood cholesterol levels, decrease heart disease risks, and manage mood.

2. Among the options, walnut oil is known to be a rich source of polyunsaturated fats. It contains a high amount of omega-3 fatty acids, a type of polyunsaturated fat that is beneficial for heart health.

3. Green beans, whole milk, and roast beef do contain fats, but they are not as high in polyunsaturated fats as walnut oil. Green beans are low in fat overall, whole milk contains more saturated fat, and roast beef, while it does contain some polyunsaturated fat, it also contains a higher amount of saturated fat.

So, the answer is Walnut oil.