Seasons are celebrations a years ferris wheel. both honor our worlds habit of spinning 'round a star which one of the following sentences best express the main idea of this poem

1. in which sentence is the underlined portion a predicate nominative? for astronauts, going into space to repair orbiting equipment becomes a challenge. for astronauts, going into space to repair orbiting equipment becomes tricky. for astronauts, going into space to repair orbiting equipment becomes challenging. for astronauts, going into space to repair orbiting equipment becomes frequent.