Read the following context and choose the best option to answer the question.
Context: Alex the African grey parrot lived and was studied for 30 years before his death last year . His researchers taught him english and then tested his reasoning abilities . In one test Alex was presented with a tray on which lay a green key and a green cup .
Question: What may be the reason Alex the African Grey was appreciated in life ?
Options: 
- Researchers were able to learn much about how the mind of an older Macaw works .
 - The knowledge that was gained by working with him is invaluable .
 - Alex was able to teach his researchers much about birds in his 20 years of service .
 - None of the above choices .


The knowledge that was gained by working with him is invaluable .