Option A is correct. 'Taking advantage of the shaky situation' is close in meaning to the required one. Thus, it is the correct answer.
Option B is incorrect. It does not have the required meaning and so, it is incorrect.
Option C is incorrect. The shopkeepers were not necessarily troubling others. Thus, it does not have the required meaning.
Option D is incorrect. They were not involved in black marketing. Thus, it is incorrect.