19.
(A) casual
(B) similar
(C) direct
(D) grateful

    Hiding herself among the trees near a chimpanzee habitat, Elizabeth Lonsdorf is using her camera to explore mysteries of learning. The chimpanzee she records picks up a thin flat piece of grass and then digs out tiny insects from a hole. Dinner is 16 ! But how did the chimp develop this ingenious skill with tools? Do the chimp babies copy their parents in using tools? Do the mothers most skilled with tools have offspring who are also good at using tools? Here in Africa, Lonsdorf is conducting one of the world's longest wildlife studies, trying to discover how learning is transferred 17 generations. 

    Lonsdorf has always been interested in animal learning and tool use, 18 the way young animals grow up and learn their way in the world. Her chimpanzee study shows a clear link between humans and the rest of the animal kingdom. The chimps make and use tools and have mother-child relationships very 19 to those of humans. Through observing chimpanzees' learning process, researchers hope to gain insight into what the development of our earliest ancestors 20 like. 

    Lonsdorf hopes that by understanding the complexity of animal behavior, we can better appreciate and protect the diversity of life on this planet.