Regarding the use of commas, which one of the following statements is accurate?
a. there is no need for commas that indicate added details in a sentence.
b. a parenthetical use of commas is usually confusing to the reader.
c. commas are needed to separate a list of three or more items in a sentence.
d. you should not use a comma to separate two complete sentences joined by "and."

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.