Fill each blank with a suitable word to complete the following passage.

Space exploration is the investigation of the universe beyond the Earth’s atmosphere, by (1) ________ of manned or unmanned spacecraft. Despite the technological advancements achieved in the past, space exploration was only (2) _______ until the 20th century. The first successful orbital launch was made by the Soviet Union in 1957 which was called “Sputnik”. When the topic “SPACE EXPLORATION” is put (3)_______ the table, a question has often been asked: “Why should we spend money on NASA while there are so (4) _______ problems here on Earth?” However, this might be partially wrong since exploring the unknown may help us progress.

The advantages of space exploration include the materials (5) ________ can be obtained from outer space. For instance, asteroids have iron and nickel which could be utilized to satisfy the (6) ________ for metal. Therefore, numerous commercial companies have invested in developing technology for asteroid mining. Several comets and asteroids (7) ________ solid water in them. This water can be used for astronauts and scientists in space stations. The water can also be broken down to hydrogen which can be used as (8) ______ for the rockets. Scientists also believe that dinosaurs disappeared because they couldn’t go to (9) ________ planet. Sooner or later a killer comet will again cross Earth’s path, threatening all life. Fortunately, (10) _________we have knowledge about comets and space science, we will be able to survive.

Question 4: