Analysts Have Puzzled Over Why Carry Trade Profits Persist

Analysts have puzzled over why carry trade profits persist. They have rejected all the following explanations, EXCEPT:

A) trade costs in financial markets are sufficiently high enough to make arbitrage impossible.
B) when traders buy or sell an asset in large volumes, it may move the price sufficiently to cause independent changes in the exchange rate.
C) risk of exchange rate movements is so large that many traders prefer not to engage in arbitrage in these markets for fear of excessive losses.
D) there may be a substantial difference in the bid-ask prices of currency that make arbitrage less profitable.