Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks.
PLANET EARTH
Planet earth is part of a system of planets and their moons, as well as numerous asteroids and comets which ___(1)___ around a huge star we call the Sun. The Sun itself ___(2)___ of gas. Nuclear reactions inside its core produce the heat and light that make life on the Earth ___(3)___. The Earth is the third of four small terrestrial (Earth like)planets. Further out in our Solar System are four huge gas planets, while distant Pluto, the smallest planet, is made ___(4)___ rock and ice. Our Earth is one of the ten planets that orbit the Sun- a huge, burning-hot star in the center of our Solar System. The Solar System and all the stars in the ___(5)___ are part of our galaxy-the Milky Way, ___(6)___ contains as many as 200 billions stars. Beyond our galaxy are millions more galaxies. They all add together to make up the Universe.