Choose the word which best expresses the opposite meaning of the word.
SAPIENT

Let's look at the meanings of the given word and marked option: 
Sapient- having or showing deep understanding and intelligent application of knowledge 
foolish- showing or marked by a lack of good sense or judgment 
Let's look at the meanings of the other given options: 
wise- having or showing deep understanding and intelligent application of knowledge 
wasteful- given to spending money freely or foolishly 
culvert- a transverse drain 
Hence from the given meanings, we find that foolish and Sapient are antonyms.