Reread paragraph 2 and 3 of the article. whist phrase in paragraph 3 hints at the meaning of the words perceiving and perception from paragraph 2?

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.