Answer: b

Analyzing item A, in the process of trading a futures contract, when the contract price rises and falls continuously in the same direction, there is a national legal holiday, or the exchange thinks that the market risk has changed obviously, the exchange can adjust the range of its price limit according to the market risk; For item C, generally speaking, for varieties and contracts with large fluctuations in futures prices, the price limit is correspondingly large; Item d, the price limit system can lock the maximum profit and loss of the contracts held by members and customers on each trading day, creating favorable conditions for the implementation of the deposit system and the debt-free settlement system on the same day.