Input: Identify the most salient words:

white clouds forming on the blue sky in the morning

Output: cloud
form
morning

Input: Identify the most salient words:

a helicopter flies south as planes and helicopters attack a fire approaching

Output: fly
helicopter
plane

Input: Identify the most salient words:

biological species growing up a tree

Output: grow
specie
tree

Input: Identify the most salient words:

doctors taking notes about a scan at the hospital

Output:
doctor
hospital
note
take