Questions 15 - 17 (Two blinking LEDs)

void setup()
{
  pinMode(12, OUTPUT);
  pinMode(13, OUTPUT);
}

void loop()
{

  digitalWrite(13, HIGH);   // Turn on pin 13 LED
  digitalWrite(12, LOW);    // Turn off pin 12 LED
 
  delay(1000);              // Wait for one second
 
  digitalWrite(13, LOW);    // Turn off pin 13 LED
  digitalWrite(12, HIGH);   // Turn on pin 12 LED
 
  delay(1000);              // Wait for one second
}