防御地球(Defends Earth)

"Defends Earth" challenges you to survive to 50 waves of alien attacks on our planet. 
The alien ships are piled around the Earth, you should avoid impacts, counterattack with your own weapons and return alien´s shots for the survival of mankind. 
"Defends Earth" is easy to play for those who do not usually play this type of game and a challenge for those experts who want to survive the 50 waves. 
Very few have succeeded, do you dare to be one of them? 
TRY IT!