Question

Andrea Ghez is a respected astronomer. She believes that a black hole exists in our galaxy.
Combine the two sentences by adding an appositive or appositive phrase and punctuating accordingly.

Answer 1

The correct sentence would be:

Andrea Ghez, a respected astronomer, believes that a black hole exists in our galaxy.

Answer 2

An apositive phrase is also known as noun phrase which serves the purpose of providing additional information about the noun and identifies it. In this case we are talking about Andrea Ghez. If we combine the two sentences given, we would have: Andrea Ghez, who is a respected astronomer, believes that a black hole exists in our galaxy. The relative pronoun "who" and "is" can be dropped without affecting the idea.