TASK 25. Revision: adjectives and adverbs. Use the best suitable word in each gap

Whether or not we are alone (1) in the universe is a question that has vexed humankind for centuries. But we are lucky/fortunate (2) to live in an era when the technology exists to allow us to come close/near (3) to giving an answer. Up to now, not (4) only was a belief in the existence of extraterrestrial life often based (5) on personal rather than religious conviction, it (6) was perhaps as (7) much based on faith. But scientifically the possibility cannot be discounted and, perhaps more than (8) at any other time in history, the subject is no longer liable to (9) be dismissed as a crank's discipline. For example, can we estimate the number of civilisations within our own Milky Way galaxy? These days scientists believe that in some way/ways/respect (10) they now have a not inconsiderable/insignificant (11) knowledge of the factors involved in producing such civilisations. The rate of formation of suitable stars - that is, ones like (12) Earth which are hot enough (13) to sustain life and live long enough to allow life to evolve - is a good/reasonable (14) starting point. Astronomers are confident that (15) they can assess this rate of formation at about (16) one star per year. However, these stars also need to have habitable planets. Only (17) in the last five years have scientists found evidence that at least some stars (other than our own star, the sun) have planetary systems. Broadly speaking (18), perhaps one in ten stars have planets orbiting them. But we also require that these planets are warm enough to have liquid water, a basic component integral to (19) life on Earth and presumably life elsewhere, and are not lacking in (20) an atmosphere that can both provide protection and sustenance to developing life.