Final answer:
Humans are least closely related to gibbons.
Step-by-step explanation:
The correct answer is d. gibbon.
The question asks which animal humans are least closely related to. Based on the given information, humans are most closely related to chimpanzees and bonobos, which are both species of great apes. The article states that gorillas, chimpanzees, and humans have more than 97% of their DNA in common, indicating a close genetic relationship. Gibbons, on the other hand, are lesser apes and not closely related to humans. Therefore, humans are least closely related to gibbons.