Final answer:
The correct answer is option C. Significant barriers to entry.
Step-by-step explanation:
The characteristic that does not apply to perfectly competitive markets is C. Significant barriers to entry. In a perfectly competitive market, many sellers and buyers participate, offering homogeneous products, and participants have perfect information about these products.
Additionally, one of the hallmarks of a perfectly competitive market is the ease with which firms can enter and exit the market, meaning that there are no significant barriers to entry. Significant barriers to entry are associated with non-competitive markets such as monopolies, where such barriers prevent competitors from entering and challenge the notion of perfect competition.