And if mark to market, they create a loss.

如果按市值计算， 他们会造成损失。

Only very large banks must mark to market all of their bonds that are available to trade.

只有非常大的银行必须将其所有可用于交易的债券按市价计价。

If you buy another bank, you then have to take mark to market on everything, all of its assets, ie the loans it's made.

如果你收购了另一家银行的话，那么你必须对其所有资产（即贷款）按市值计价。