Input: Identify the most salient words:

the total number of protons and neutrons in the nucleus of an atom

Output: atom
neutron
nucleus
number
proton

Input: Identify the most salient words:

Several skiers leave tracks while gliding across the snow.

Output: glide
skier
track

Input: Identify the most salient words:

small boat in the sea with city on horizon

Output: boat
city
sea

Input: Identify the most salient words:

close up of a beautiful slug moving slowly on the tree trunk green moss

Output:
close
move
tree