Read the following article, ignoring the empty spaces (1-5) for the time being. Then, check the alternative in which all the…

Read the following article, ignoring the empty spaces (1-5) for the time being. Then, check the alternative in which all the spaces have been CORRECTLY filled:

(1) __________ we have become accustomed to the idea of space travel, and in films and fiction it seems as tough space travel is inevitable, it appears unlikely that human beings will ever get any further than Mars, our nearest neighbor. No matter how many films we make about space travel, the fact is that it remains technologically challenging, and extremely expensive. (2) __________ the distances involved are immense, any voyage outside the solar system would take hundreds of years using current technology. Wherever human beings went into space, they would have problems of how to eat and breathe, and their spaceship would have to carry vast amounts of fuel (3) __________ cover the distance. Even Mars is so far away that it would take about six months to get there. (4) __________ the distance between Earth and Mars varies, astronauts would have to wait for nearly two years before they could return using the shortest journey time. (5) __________ it could cost as much as $ 100 billion, a manned mission to Mars is planned for sometime between 2010 and 2020.