Internship Opportunities - what to do?

So recently I applied to three internships regarding various animals. One is with marine animals and the military, one is with cats and other mammals in a small sanctuary, and one is at a big zoo. I recently got offered the position at the small sanctuary, but have still been waiting to hear back from the other internships but I have to let them know if I am accepting the position or not. Should I accept it and then decline it if I get the better opportunity or should I decline? What should I do!

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