Which of these fits gap 21?

Directions: Complete this passage by selecting the most suitable option for the corresponding gap.

A day at the zoo is a _____(21)_____ experience. You see all kinds of animals there. Lions, elephants, snakes, turtles, foxes, pandas, wolves, raccoons, you name them and you got them. You can see all kinds of animals whether they are ______(22)_____ or common, for the state allows a zoo to keep such animals. Great animal _____(23)____ take care of them in a zoo. In a circus, we have lots of fun. But, only those animals that are ______(24)______ enough to show tricks can be seen in a circus.