III. Choose the word that best fits the blank space in the following passage. (1.5 pts)

Moments in space history
On October 4,1957, the Soviet Union sent Sputnik 1 into space and a new age in history began - The Space Age. The Soviets (17) ________ more Sputnik satellites in the fifties and by 1961 they had put the first man into space. Eight years later, an American finally walked on the moon, and during the (18) _______ seventies the US led the Soviet Union in the space race. However, space travel was expensive, and they needed to co-operate more. Nearly two decades later, leaders from both countries said they had agreed (19) ________ plans for a new International Space Station (ISS), and by the turn of the century the ISS had started (20) ________ the Earth. Nowadays, the ISS is used by scientists from all over the world.
At the beginning of the twenty-first century, businessman Dennis Tito told the world he loved space as he spent eight days on the ISS. Since then, space (21) ________ has developed with plans for regular tours and floating hotels. And what about the next half a century? In 2010, the US president Barack Obama told (22) ________ that by the mid-2030s the US would send humans to Mars. The race for Mars has already started.
Adapted From “Life - Pre-Intermediate Student’s Book"