Question

The curator of the art museum, _____ gave a speech last night, will be attending tonight's ceremonies, as well.

Answer 1

Answer:

B.) Who

Explanation:

The curator of the art museum, who gave a speech last night, will be attending tonight's ceremonies, as well.

The term "that" is a less formal way to put it. And using the term "which" does not make grammatical sense, so your best choice would be "who".

Answer 2

The curator of the art museum, who gave a speech last night, will be attending tonight's ceremonies, as well.