单选题 A market is said to have external or informational efficiency if it features:

A、 market prices that reflect all available information about the value of the securities traded.
B、 timely and accurate information about past transactions and current supply and demand conditions.
C、 many buyers and sellers that are willing to trade at prices above and below the prevailing market price.

【正确答案】 A

【答案解析】[解析] 信息效率(外部效率)是指市场价格会根据新的信息迅速做出调整，从而市场通行价格反映了所有可以获得的与特定资产有关的信息。因此，本题的正确选项为A。