Answer: threat of new entrants will prevent the prices from rising above the competitive level.
Step-by-step explanation:
A contestable market has competition such that sellers cannot unilaterally decide to sell at a certain price. They have to sell at a competitive price that is set by the market to ensure that goods are allocated efficiently.
If the prices attempt to rise above this competitive level, new sellers will enter the market so as to make a profit which would have the effect of driving the price back down to where it was and even lower if even more sellers come in. The price is therefore maintained to ensure that this does not happen.