Some scientists were working in a spaceship in outer space. They looked out of the ________ of the spaceship. They could ________ the planet Earth. It looked like a blue and white ______. Scientists ________ very powerful cameras. They took many ________ of our planet from outer space. The photos were very ________. The scientists were surprised at ________ they saw.

In the photos, they saw land, blue sea and ________ clouds. Some scientists said they could see a ________, dark line on the yellow earth. They thought it ________ the Great Wall of China! Do you think so?