问题如下：
The bid–ask spread for very liquid, high-volume ETFs will be least influenced by the:
选项：
A.market maker’s desired profit spread.
creation/redemption fees and other direct costs.
likelihood of receiving an offsetting ETF order in a short time frame.
解释：
B is correct. ETF bid–ask spreads are generally less than or equal to the combination of the following:
■ ± Creation/redemption fees and other direct costs, such as brokerage and exchange fees
■ + Bid–ask spread of the underlying securities held by the ETF
■ + Compensation for the risk of hedging or carrying positions by liquidity providers (market makers) for the remainder of the trading day
■ + Market maker’s desired profit spread
■ – Discount related to the likelihood of receiving an offsetting ETF order in a short time frame
For very liquid and high-volume ETFs, buyers and sellers are active throughout the trading day. Therefore, because most of these ETF trades are matched extremely quickly and never involve the creation/redemption process, the first three factors listed do not contribute heavily to their bid–ask spreads. So, creation/redemption fees and other direct costs are not likely to have much influence on these ETFs’ bid–ask spreads.
老师c选项为什么不正确。交易活跃，所以很容易匹配订单，所以discount就比较小，所以就受到的影响就比较小啊？
