中文：

分级B类基金的价格下折通常发生在基金净值低于一定阈值的情况下。这个阈值通常是基金份额净值的50%，也就是说，如果基金净值下降到这个水平，那么分级B类基金的价格就会下折。

具体来说，如果基金净值下降到这个阈值以下，分级B类基金的价格将会被强制向下折算，折算后的价格将会等于基金份额净值的一半。这种折算机制可以保护分级B类基金投资者的利益，避免其因为基金净值的持续下跌而遭受过大的损失。

需要注意的是，分级B类基金的价格下折并不是一个必然会发生的事情。如果基金净值能够逐渐恢复或者上涨，那么这种折算就不会发生。因此，投资者在投资分级B类基金时，需要充分了解其风险和特点，并且根据自身的风险承受能力和投资目标进行投资决策。

英文：

The price reduction of Class B funds usually occurs when the fund's net value falls below a certain threshold. This threshold is usually 50% of the fund's net asset value per share. In other words, if the fund's net value falls below this level, the price of Class B funds will be reduced.

Specifically, if the fund's net value falls below this threshold, the price of Class B funds will be forced to undergo a downward valuation, resulting in a price equal to half of the fund's net asset value per share. This valuation mechanism can protect investors in Class B funds from excessive losses caused by the continuous decline in the fund's net value.

It should be noted that the downward valuation of Class B funds is not a certainty. If the fund's net value can gradually recover or rise, such a valuation will not occur. Therefore, investors need to fully understand the risks and characteristics of Class B funds, and make investment decisions based on their risk tolerance and investment goals.