a signal receptor的用法和样例：
- The difference between black and yellow color in Labrador retrievers stems, for instance, from a single base change that inactivates a signal receptor in the pigment cells of yellow dogs.
- A red light is usually a signal of danger.
- The rise in prices was a signal for rebellion.
- Her speech yesterday was a signal that her views have changed.
- I'll cue you in (ie give you a signal to start) by nodding my head.