The correct answer is: A. age = 21;
Option A assigns the number 21 to the age variable.
Option B assigns the number 21 to the memory location pointed to by the age variable. This will not change the value of the age variable itself.
Option C assigns the address of the age variable to the agePtr pointer. This will not change the value of the age variable itself.
Option D assigns the number 21 to the memory location pointed to by the agePtr pointer. This will not change the value of the age variable itself.
Option E is incorrect because it includes both Option A and Option D. Option A is the only option that will assign the number 21 to the age variable.