Single out animal sanctuary, English branch first (7)
I believe the answer is:
earmark
'single out' is the definition.
The definition and answer can be both related to thinking as well as being verbs in their base form.
Maybe they are linked in a way I don't understand?
'animal sanctuary english branch first' is the wordplay.
'animal sanctuary' becomes 'ark' (I can't justify this - if you can you should give a lot more credence to this answer).
'english' becomes 'e' (abbreviation).
'branch' becomes 'arm' ('arm' can be a synonym of 'branch').
'first' is a charade indicator (letters next to each other).
'e'+'arm'='earm'
'ark' put after 'earm' is 'EARMARK'.
Can you help me to learn more?
(Other definitions for earmark that I've seen before include "Set aside for future use" , "Set aside specifically" , "spot where The Ring may be put on?" , "Allocate for a purpose" , "Set aside for a specific purpose" .)