Through observing chimpanzees' learning process, researchers hope to gain insight into what the development of our earliest ancestors 20 like.
答案：(C) might have been
【時態／語態】might have been like 表示對過去（人類最早祖先）狀態的推測，語意為「可能曾經是……的樣子」。is to be／was to be 語意不合此處對久遠過去的臆測；will have been 為未來完成式，與探討史前祖先的過去時序矛盾。
四個選項都是 be 動詞的不同形態排在一起，你會立刻認定這是時態題，開始比對前後其他動詞的時態。方向沒錯，但真正的線索不在別的動詞身上，在 our earliest ancestors 這幾個字上。
先把句型還原：what something is like 是問「某樣東西是什麼樣子」，句尾那個 like 是介系詞，前面的 what 正是它的受詞——這也是為什麼句尾的 like 不能拿掉。接著決定時態：談的是 our earliest ancestors（人類最早的祖先）的發展，那是極久以前的事，沒有人親眼看過，只能推測，所以要用對過去的推測 might have been（可能曾經是）。填進去讀成 what the development of our earliest ancestors might have been like。鑑別度只有 32，但它本身不難：might have ＋ 過去分詞是課本教過的常見組合，各種程度的人都答得出來，題目自然分不出高低。
is to be 與 will have been 都指向未來，但祖先的發展是過去的事，方向相反；was to be 是「注定要、預定要」，站在過去往後看、講的是後來果然發生的事（He was to become a famous scientist.），這一句不是在講後來發生了什麼，而是在推測當時的樣子。三個都是 be 的形態，形態吻合，容易被順手選走。
might have been（可能曾經是，對過去的推測）、What is he like?（他是什麼樣的人？）、gain insight into（深入了解、看出門道）、be to V（注定要、預定要）、through V-ing（藉由做某事）、observe（觀察）。
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.