Listen to the explanations again, and then fill in the blanks with words you hear. 听录音填空。 1.When asteroids hit the planet, they can cause _______and may cause a _______________. 2.Encke's Comet was ____________ in 1908, and it's possible that ____________________ and hit the earth. 3.Some people believe that a spaceship _____________________ in Siberia and _________________. 4.Extraterrestrials might have wanted to ______________, so they aimed their weapons at Earth and ____________________. 5.A man named Nikola Tesla tried to build a "supergun" that _____________. Maybe it was _________________ and it didn't work correctly.