When my interest shifted from space to the sea, I never expected it would cause such confusion among my friends, yet I can understand their feelings. As I have been writing and talking about space flight for the best part of 20 years, (1)___________. To explain, I’d like to share my reasons behind this unusual change of mind. The first excuse I give is an economic one. (2)_____________. The first round-trip ticket to the moon is going to cost at least 10 billion dollars if you include research and development. By the end of this century, the cost will be down to a few million. On the other hand, (3)_______________. My second argument is more philosophical. The ocean, surprisingly enough, has many things in common with space. In their different ways, both sea and space are equally hostile. If we wish to survive in either for any length of time, we need to have mechanical aids. The diving suit helped the design of the space suit. The feeling and the emotions of a man beneath the sea will be (4)____________
