3. What sentence type is this?

Generally speaking, teachers at this institution need to undertake, of their own accord of course, supplementary training courses outside of school hours in order to enhance their skills and methodologies and to meet the demands of a new generation of students.

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.