Answer:
C. Emily's sister gave birth to two twins.
Step-by-step explanation:
A redundancy is when you say something two times in the same sentence, using different words that express the same, form example in the sentence, it says that Emily´s sister gave birht to two twins, when you are saying that she gave birth to twins you already know that there were two of them, you don´t need to say two twins, that´s a redundancy.