A foil is the near complete opposite of the main character (whichever character they want you to find a foil for).
Rainsford and Whitney were good hunting friends with numerous similar interests. They could not be foils because of how close in similarity they were. Even when they disagreed on how animals felt about being hunted, Whitney seemed open to and intrigued by Rainsford's points and way of thinking.
Ivan is a near irrelevant character, being a mere Cossack who follows whatever General Zaroff says. He is mindless and has almost zero traits to even compare to Rainsford, let alone any traits aside from a mindless follower to begin with.
The answer would be General Zaroff. This is almost like the cliche protagonist vs antagonist foil. Both of them are hunters, but different kinds. Zaroff got bored with animals and wanted to hunt human people instead, whereas Rainsford had enjoyed the thrill of an animal hunt and thinks that the hunting of people is murder. Zaroff is more heartless and cold, a killer, if you will. Rainsford seems to think highly of actual people, and had no interest in playing Zaroff's game.
Alifa Rifaat's short story "Another Evening at the Club" paints a clear picture of the powerless, inferior role of women in Egyptian society: the main character Samia is trapped in an arranged marriage in which she is repeatedly forced into betraying her own values and beliefs.
For example, when Bey, her husband, says to Samia "Tell people you're from the well-known Barakat family and that your father was a judge," she is obliged to lie about her own family's social status, in spite of how she was raised to be an honest person, just for the sake of making Bey look more important in the public eye.
In the end, Bey forces Samia into the ultimate act of dishonesty: protecting a lie that is causing their servant to be tortured, only to avoid his husband's embarrassment, when he says "By now the whole town knows the servant stole the ring—or would you like me to tell everyone: 'Look,folks, the fact is that the wife got a bit tiddly on a couple of sips of beer and the ring took off on its own and hid itself behind the dressing-table."
