Answer : 1. "Barrel"
Explanation :

Answer: A) Barrel Explanation: Here Thread and String are Synonyms of each other. Then the answer will be the synonym of Cask.  Cask is nothing but a large barrel-like container used for storing liquids, typically alcoholic drinks.  Ex : Drum, Vessel, Tank, Barrel, Hogshead, Firkin,...   Here from the options Barrel is the only synonym of Cask.   Thus,  Thread : String :: Cask : Barrel