He began his career as a zoologist, 28 mollusks and their adaptations to their environment.
答案：(C) studying
現在分詞 studying 引導分詞片語，補充說明他身為動物學家時所做的事（研究軟體動物），與主要子句主詞 He 是主動關係。study（原形）、studied（過去式，不能單獨作分詞片語）、being studied（被動語態，語意錯誤——他是研究者不是被研究對象）皆不合。
四個選項是同一個字 study 的四種形態，你會直覺開始找主詞、判主動被動。
先看逗號前面：He began his career as a zoologist 已經是一個完整的句子，主詞 He、動詞 began 都在。逗號後面不能再放一個限定動詞，所以 study 與 studied 先出局。剩下 studying 與 being studied，再判方向：研究軟體動物的是皮亞傑本人，他是主動去研究，不是被研究，所以用現在分詞 studying。填進去讀成 He began his career as a zoologist, studying mollusks and their adaptations to their environment（他以動物學家的身分展開生涯，研究軟體動物以及牠們對環境的適應）。這就是分詞構句：分詞的意義主詞與主要子句的主詞是同一個人，用來補充說明他同時在做什麼。
study 與 studied 都是限定動詞，前面沒有連接詞就不能接在一個完整句子後面；being studied 是被動，方向剛好相反——軟體動物才是被研究的那一方。
分詞構句（分詞的意義主詞與主要子句的主詞相同）、現在分詞表主動、過去分詞表被動、begin one's career as（以……的身分展開職業生涯）、adaptation to（對……的適應）、mollusk（軟體動物）。
Jean Piaget, a psychologist and pioneer in the study of child intelligence, was born in Switzerland in 1896. At age 10, he managed his first 26, a description of a partly albino sparrow he observed in a public park. At age 15, he 27 to devote his life to developing a biological explanation of knowledge.
He began his career as a zoologist, 28 mollusks and their adaptations to their environment. 29 age 21, he had already published 25 professional papers on that topic.
Later, after working with Alfred Binet in Paris, he became interested in levels of logic used by children taking standardized tests on intelligence. Piaget 30 to establish a body of psychology all his life and became a very influential figure in educational psychology. His works were all written originally in French and were later translated into English.