kanishaksharma
No explanation presented is possible without using idioms, is there any other way ?
Nothing here relies on memorized idioms.
The three middle choices (B, C, D) are ungrammatical, because they follow
about—a preposition—with a complete sentence. (Like other prepositions,
about can only be followed by a noun.)
Between A and E, you should notice that choice E uses an __ING modifier that takes the following subject as the subject/agent of the __ING action (Who was "referring to the current hostility"? Smokers were). Choice A, on the other hand, uses an impersonal construction, implying that the smokers were NOT personally involved in that part.
In this context,
the smokers were "referring to the current hostility" (which was the basis for their anxiety, as described later in the sentence), so E makes sense and A does not.