问题如下：
An arbitrageur will most likely execute a trade when:
选项：
A. transaction costs are low.
B. costs of short-selling are high.
C. prices are consistent with the law of one price.
解释：
A is correct.
Some arbitrage opportunities represent such small price discrepancies that they are only worth exploiting if the transaction costs are low. An arbitrage opportunity may require short-selling assets at costs that eliminate any profit potential. If the law of one price holds, there is no arbitrage opportunity.
C项可否理解为，因为一价原则，最终两个市场的相同标的会收敛，所以才去做套利交易。