Scenario $1$: Consider a simple pricing game in which two firms can each choose whether to undercut their opponent or not. We will assume the firm with the lowest price gets the entire market, and if the prices are identical they will share the market. Note the Nash Equilibrium of this game is $($Low Price, Low Price$),$ and each Firm will receive a payoff of $1.$ However, if they could both agree to set a high price $($i$.$e$.$ collude$),$ they would each receive a payoff of $2.$ The problem lies in the fact that each Player has an incentive to $$cheat$$ and set a lower price, so the Firms end up in a price war.

Refer to Scenario $1.$ Considering how each option will change the payoffs of the game $($and ultimately the Nash Equilibria$),$ which of the following would make collusion $($both firms setting a high price$)$ a possible Nash Equilibrium?

Choice $1$ of $4$:a$.$ Increased advertising expenditures increase the demand for the products.Choice $2$ of $4$:b$.$ Each firm implements a price$-$match guarantee. Specifically, if one firm sets a low price, the other firm will automatically match it$.$Choice $3$ of $4$:c$.$ Firm $1$ implements cost$-$saving measures, ensuring higher payoffs.Choice $4$ of $4$:d$.$ All of the above could result in a Nash Equilibrium of $($High Price; High Price$).$