The chimps make and use tools and have mother-child relationships very 19 to those of humans.
答案：(B) similar
similar to those of humans（與人類的相似）表示黑猩猩的親子關係與人類非常相似；casual（隨意的／非正式的）、direct（直接的）、grateful（感激的）均不符合 similar to 的固定搭配語意。
四個選項都是形容詞，都能擺在 very 後面，你會直接比中文哪一個讀起來順。
這一格靠空格後面那個介系詞就定得下來。空格後是 to those of humans，先問哪一個形容詞固定接 to 表示「與……相比」——是 similar，be similar to 是成組的說法。再看 those 指的是誰：它代替前面的 mother-child relationships，免得整組名詞再講一次，所以 those of humans 就是「人類的親子關係」。整句讀成黑猩猩的親子關係與人類的非常相似，也正好呼應前一句 shows a clear link between humans and the rest of the animal kingdom（顯示人類與其他動物之間有明顯的關聯）。
casual（隨性的、非正式的）與 direct（直接的）都不接 to 作比較；grateful（感激的）雖然也接 to，但 be grateful to somebody 接的是人、講的是感謝，與「兩者相像」無關。三個都是形容詞，形態吻合，容易被順手選走。
be similar to（與……相似）、be different from（與……不同）、those of ＋ 名詞（代替前面提過的複數名詞，避免整組重講）、mother-child relationship（親子關係）、make and use tools（製造並使用工具）、be grateful to somebody（感謝某人）。
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.