Which of the following can be used to replace /* expression */ so that getTotalMileage returns the total of the miles traveled for all vehicles in the fleet?

Consider the following interface and class declarations.

public interface Vehicle 
{
  /** @return the mileage traveled by this Vehicle */
  double getMileage();   
}

public class Fleet 
{
  private ArrayList<Vehicle> myVehicles; 

  /** @return the mileage traveled by all vehicles in this Fleet */
  public double getTotalMileage() 
  { 
    double sum = 0.0; 
    for (Vehicle v : myVehicles) 
    { 
      sum += /* expression */ ; 
    } 
    return sum; 
  } 
  // There may be instance variables, constructors, and methods that are not shown. 
}

Which of the following can be used to replace /* expression */ so that getTotalMileage returns the total of the miles traveled for all vehicles in the fleet?