The word that is a synonym of entertain as it is used in this sentence from the passage is B. Think.
According to the dictionary, another meaning of the word entertain, apart from the well-known "provide (someone) with amusement or enjoyment", is to "give attention or consideration to (an idea or feeling)." That is to say, to consider, give consideration to, take into consideration, think about, contemplate, give thought to, bear in mind, etc.
