game_ functions py def check_aliens_bottom(ai_settingsscreenstatssbshipaliensbullets)"""check if any aliens have reached the bottom of the screen ""screen_rect screen get_rect(for alien in aliens sprites()if alien rect bottom >screen_rect bottomtreat this the same as if ship got hit ship_hit(ai_settingsscreenstatssbshipaliensbulletsbreak now check_aliens_bottom(accepts sb as parameterand we add an sb argument in the call to ship_hit(finallypass sb in the call to update_aliens(in alien_invasion pyalien_ invasion py start the main loop for the game while true--snip-if stats game_activeship update(gf update_bullets(ai_settingsscreenstatssbshipaliensbulletsgf update_aliens(ai_settingsscreenstatssbshipaliensbullets--snip-figure - shows the complete scoring system with the remaining ships displayed at the top left of the screen figure - the complete scoring system for alien invasion