The answer to your question would be that the sentence that includes a restrictive clause is the following one: The ceramic cups Birgit bought at the garage sale are all chipped.
The sentence above contains a reduced relative clause because it does not contain the relative pronoun (a). What is more, it is restrictive because it adds essential information to the sentence; it helps identify the noun it modifies (the ceramic cups Birgit).
a) The ceramic cups Birgit which were bought at the garage sale are all chipped.