Answer:
counter-act one another.
Step-by-step explanation:
As a bilateral monopoly has one buyer and one seller, the buyer wants to pay the lower price possible and the seller wants to charge a high price. So, they have opposite goals and they have to negotiate considering the power each one has and find an agreement in which both win. According to this, the answer is that in a bilateral monopoly with one buyer and one seller, the monopoly power of the seller and the monopsony power of the buyer tend to counter-act one another as their positions are in conflict and they have to find a middle point to get to an agreement.
The other options are not right because their goals are in conflict so they don't support the idea of the other party and both parties have a relative bargaining power and because of that, the monopoly power of the parties does not favor the buyer or the seller.