Assertion (A) : Though height and body build are primarily inherited characteristics, good nutrition and exercise also make a difference.
Reason (R) : Heredity and environment interact in their effects on development.
Choose the correct option :

The correct option is Both (A) and (R) are true and (R) is the correct explanation of (A).

Step 1: Analyze Assertion (A)
Assertion (A) states: "Though height and body build are primarily inherited characteristics, good nutrition and exercise also make a difference."
Height and physical build are strongly influenced by genetic factors (heredity) inherited from parents. However, environmental factors such as adequate nutrition, access to healthcare, physical activity, and overall lifestyle significantly impact whether an individual reaches their full genetic potential. Therefore, Assertion (A) is true.

Step 2: Analyze Reason (R)
Reason (R) states: "Heredity and environment interact in their effects on development."
Human development is not determined solely by nature (heredity) or nurture (environment) in isolation, but by a continuous dynamic interaction between both factors. Genetic traits set the potential parameters, while environmental conditions determine how these traits manifest. Therefore, Reason (R) is true.

Step 3: Evaluate the Connection between (A) and (R)
Assertion (A) gives a specific, practical example of how genetic predisposition (inherited height/body build) works together with environmental influences (nutrition and exercise). Reason (R) states the broad psychological and biological principle governing this phenomenon—namely, that heredity and environment interact to shape human development. Thus, Reason (R) directly explains why both genetic and environmental factors influence physical features as stated in Assertion (A).

Consequently, both statements are true, and (R) is the correct explanation of (A).