Really it all depends but for animals rights you can do a dramatic opening like "This is how scientist really test on animals"
If we are going to search the meaning of the word "austere" in the dictionary or any reliable sources, we will see that this means severe or strict in manner or unemotional, etc. From the words used in the sentence, another word that has similar meaning to the word "austere" is the word "stern". Thus, the answer to this item is stern.
D. because a custom is like a tradition