The nonhuman species that has made the most spectacular progress toward learning to communicate by an approximation of human language is the a. dolphin b. gorilla c. common chimpanzee d. bonobo chimpanzee

The answer is "d. ​bonobo chimpanzee".

Researchers have depicted the correspondences of chimpanzees and bonobos in new and unbeatable detail, offering a dictionary for our nearest living relatives and even a look into the starting points of human language. Humans are similarly identified with bonobos and basic chimpanzees, sharing a typical precursor that lived around 7 million years back.