13. Children learn languages best when they start at a very young age. There is no better time for children to learn language ___ they are very young.
• Then when
• Whenever
• That when
• If

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.