Answer:
Frank Inn trained animals to be actors.
Step-by-step explanation:
A topic sentence should be concise and an instant summary of what follows in the paragraph. The ideal answer would be one that encompasses what the paragraph details.
While I do agree with Epictimegamer's point on looking at the perspective of the paragraph on a whole, the focus should mainly be on what a topic sentence is supposed to be. Not vague, but instead short and sweet to the point of the reading.
Hope this helps!