Read the following passage and do as directed.

Research on animal behavior shows that many species have deeper emotions and cognitive abilities than we once thought. In the past, animals were believed to act purely on instinct, but modern studies reveal that they have inner lives with thoughts and feelings similar to ours.

Primatologist Dr. Jane Goodall’s research on wild chimpanzees in Africa challenges those old assumptions. She observed that chimps laugh when they play and cry when they grieve, showing emotions like joy, sadness, fear, and playfulness. For example, Goodall documented mothers comforting their frightened young by hugging and grooming them. She also noticed that after conflicts, adult chimps would groom or sit close together to maintain peace and strong bonds within their group. Yet, chimpanzees in captivity, deprived of social interaction, often succumb to depression and emotional illnesses that can be hard to overcome. As intelligent social animals, they also need companionship.

Goodall’s groundbreaking observations remind us to respect the emotional lives of chimpanzees and other animals. Her work has not only inspired studies on animal behavior but also fueled conservation efforts and raised ethical questions about how we treat animals.

What is the verb phrase ‘succumb to’ closest in meaning to? slow down B. speed up C. suffer from D. recover from