Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the questions from 24 to 28.

The Shuttle Era Comes to an End

The set of Space Shuttle missions run by NASA captivated the world and proved that reusable spacecraft could be used to bring astronauts and cargo into space. The Space Shuttle programme had a total of six separate orbiters, five of which actually went into space. The first-made orbiter was only used to gather data about how the shuttles would glide back to the earth. This shuttle would be brought up into the air by a specially modified Boeing 747 and released to glide down without any power of its own.

The Space Shuttle Era ran from the first launch on April 12, 1981, and ended when the final shuttle landed on July 21, 2011. During this time, there were 135 missions flown. Of the five shuttles that did go into space, two met with disasters that killed all the crew members aboard.The first disaster happened on January 28, 1986 when Space Shuttle Challenger ran into severe problems and exploded less than two minutes after take-off. It was a major blow to NASA as a school teacher was on board the orbiter, and the launch was being watched by children from schools across the United States. The second disaster came on February 1, 2003. After having completed its mission, Space Shuttle Columbia was returning to the earth from space. During damage done to a wing during its launch, the orbiter disintegrated as it hit the earth’s atmosphere during re-entry.

Because the Space Shuttle programme was running, it largely made possible the construction of the International Space Station (ISS). The shuttles brought astronauts to the station, replenished supplies, and carried actual pieces to the Space Station up from the earth.As the Space Shuttle Era came to an end, many space lovers have been left wondering, “What’s next?” There is still plenty to explore, so we will all just have to wait and see.

Climate scientists now believe that (20) ______ are mainly responsible for this.