A、They are not stable. B、They are not flexible. C、They have no sense of touch. D、They cannot hold things. C

A human hand can find a tool without looking, or put down a glass of water without spilling. But for robots, these actions are harder than they seem. That is because using a hand requires a sense of touch. Veronica Santos leads the Biomechatronics Lab at the University of California, Los Angeles. She and researchers are designing robot hands that do not just hold things. The robot hands can also feel when to let go, says Kenny Gutierrez, a graduate student. " It’s waiting for contact with the table before it decides to let go of the box. " The researchers have created a mechanical finger that senses many of the same things human fingers do. Santos says the device is equipped with a sensor that provides information about what the fingertip is touching. The information can include the object’s temperature, internal fluid pressure and movement. Making robots more gentle and sensitive to touch is a popular research area. Engineers at New York’s Cornell University, for example, built a robot that can identify when a tomato is fully grown. Its sense of touch comes from light shining through its clear rubber skin. Cornell engineering professor Robert Shepherd says this technology costs less than high-tech electronic skin. Scientists at China’s Harbin Institute of Technology have made artificial skin with electronic hairs that feel pressure much like human hairs do. It can feel something as soft as a tissue. Researchers are now working to add a sense of touch to artificial arms and legs.
Questions 16 to 18 are based on the passage you have just heard.
16. Why cannot robots put down a glass of water without spilling?   
17. What are researchers at the University of California doing?   
18. What is a popular research area for robot engineers according to the speaker?