Explanation
Correct answer: B.
Choice B is the best answer. The convention being tested is the use and punctuation of an integrated relative clause. This choice correctly uses the relative pronoun “that” and no punctuation to create an integrated relative clause that provides essential information about the noun phrase (“a book packaging company”) that it modifies.
Why the other choices are wrong
Choice A
Choice A is incorrect because it doesn’t use a relative pronoun to link the verb phrase beginning with “specializes” to the noun phrase that it modifies (“a book packaging company”).
Choice C
Choice C is incorrect because it doesn’t use a relative pronoun to link the verb phrase beginning with “specializes” to the noun phrase that it modifies (“a book packaging company”).
Choice D
Choice D is incorrect because no punctuation is needed between the integrated relative clause beginning with “that specializes” and the noun phrase that it modifies (“a book packaging company”).