The artist decided to paint Gary the Snail.
In this sentence pick the common noun(s)

snail.

Explanation:

Artist is an noun not an common noun. For it to be an common noun it needs to be person at least. Gary is also an noun.  The rest are verbs or regular words.

in an effort to stem the tide of refugees attempting to leave east berlin, the communist government of east germany begins building the berlin wall to divide east and west berlin. construction of the wall caused a short-term crisis in u.s.-soviet bloc relations, and the wall itself came to symbolize the cold war.

it's