An example can be hot dogs and hot dog buns. If the price of one of them falls, it would lead to the product being cheaper which would increase sales, thus bringing the demand for the other one to be much higher.
The answer is D. persistence !
"Tragedies" is the one among the following choices given in the question that is the kind of plays written by Sophocles. The correct option among all the options that are given in the question is the second option or option "B". I hope that this is the answer that has genuinely come to your help.