**Explanation:**

Physical activity refers to any movement of the body that requires energy expenditure. It is well-known that physical activity has numerous benefits for our health and well-being. However, there are certain statements about physical activity that are not entirely true. Let's examine each statement and determine which one is not true.

**a. Physical activity may increase longevity:**
This statement is true. Numerous studies have shown that engaging in regular physical activity can increase life expectancy. Regular exercise has been linked to a reduced risk of chronic diseases such as heart disease, diabetes, and certain types of cancer, which are leading causes of death. Moreover, physical activity can improve cardiovascular health, strengthen the immune system, and enhance mental well-being, all of which contribute to a longer and healthier life.

**b. Regular exercise, regardless of intensity, makes you healthier:**
This statement is also true. Regular exercise, whether it is low-intensity or high-intensity, has numerous health benefits. Low-intensity activities such as walking, gardening, or household chores can still provide health benefits such as improved cardiovascular fitness, increased muscle strength, and weight management. On the other hand, high-intensity activities such as running, cycling, or swimming can further enhance these benefits and may also improve athletic performance. The key is to find an exercise routine that suits your fitness level and preferences.

**c. Physical activity must be a part of a regular exercise program:**
This statement is true. Physical activity should be included as part of a regular exercise program to achieve optimal health benefits. A regular exercise program typically includes a combination of aerobic exercise (such as walking, running, or cycling), strength training (such as lifting weights or using resistance bands), and flexibility exercises (such as stretching or yoga). These different types of exercise work together to improve cardiovascular health, build muscle strength, and enhance flexibility.

**d. A little physical activity is better than none:**
This statement is also true. Even a small amount of physical activity is better than being completely sedentary. Engaging in just 15-30 minutes of moderate-intensity physical activity per day can provide health benefits such as improved mood, increased energy levels, and reduced risk of chronic diseases. It is recommended to gradually increase the duration and intensity of physical activity over time to further enhance these benefits.

**Conclusion:**
After examining each statement, it can be concluded that **b. Regular exercise, regardless of intensity, makes you healthier** is NOT true of physical activity. Regular exercise, regardless of intensity, does make you healthier and provides numerous health benefits.

It's option A. physical activity may increase longevity.:-)