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 from 23 to 27. Fill in the appropriate word in question 23

  Many people enjoy lying in bed in the morning, but can you imagine having to spend 90 days in bed? Could you stand the boredom and the frustration of not being (23) _____________ to get up? That was the task that faced 14 volunteers when they started out on a bed-rest experiment being conducted (24)_____________  the European Space Agency.

  The study had a serious purpose: to investigate the changes that take place in the human body during long-duration spaceflight. Lying in a horizontal position was the best way of (25)_____________  weightlessness. The aim was to discover what effect period of weightlessness will have on the health of astronauts spending several months on the International Space Station.

  The volunteers ate their meals, took showers and underwent medical tests without ever sitting up. That’s even tougher than it sounds, especially when you (26)_____________ that no visitors were permitted. However, each volunteer did have a mobile phone, as well as access to the latest films, computer games and music. Surprisingly, Everyone was in a good (27)_____________  at the end of the 90 days, “I would do it again,” said one of the volunteers. “It was disorientating, but we knew we were ‘contributing to medical research and space exploration.”