Consider the following code fragment. Assume that the variables width, length and area have all been declared and initialized (if necessary). // compute the area of the building lot in acres computeLotInAcres(width, length, area); // Display results cout << "A building lot of " << width << " feet by " << length << " feet has " << area << " acres. "; What must be true about the area argument to the computeLotInAcres() function?

a. It is passed as a reference parameter.

b. It is a defined constant.

c. It must be declared in the computerLotInAcres() function, but not in main()

d. It is passed as a constant reference parameter.