I just can't seem to get past 4 1/2 stars whenever I try. Right now I am playing the mysterious panda campaign. all of the zoo fame bars are all the way up except for three: the challenge bar, entertaining animals bar, and educational habitats bar. I've put a ton of plants, rocks, and trees in their exhibits. I've also put a ton of toys where people look at them the most. The challenge bar is completely empty because I don't think there are challenges in campaign games. Can someone please help? Thanks.