Be gentler when developing this? (5,4)
I believe the answer is:
green belt
'this?' is the definition.
The definition suggests a singular noun which matches the answer.
'be gentler when developing' is the wordplay.
'when developing' indicates anagramming the letters (letters developed into a new form).
'be'+'gentler'='begentler'
'begentler' with letters rearranged gives 'GREEN BELT'.
Can you help me to learn more?
(Other definitions for green belt that I've seen before include "Something about London" , "Martial artist" , "status of karate?" , "protected area" , "area of open land near town" .)