Both statements made by the trader regarding the box spread options strategy are accurate. Statement I is correct because a box spread is indeed a combination of a bull spread and a bear spread. Specifically, in a box strategy, the investor holds four positions in options: a long call and a short put option with the strike price X1, and a short call and a long put with the strike price of X2. This combination of positions creates a 'box' of options that can be used to hedge risk or generate income. Statement II is also correct because the payoff of the box spread will always be X2-X1, regardless of whether the final or current price is below X1, between X1 and X2, or above X2. This is because the box spread is designed to have a fixed payoff, which is the difference between the two strike prices. This makes the box spread a risk-free strategy, as the investor knows in advance what the payoff will be, regardless of the movement in the underlying asset's price.

Choice A is incorrect. Statement I is correct as a box spread strategy indeed involves the combination of a bull spread and a bear spread strategy. This means that it includes both buying and selling call options, as well as buying and selling put options, with different strike prices but the same expiration date.

Choice B is incorrect. Statement II is also correct because the payoff of a box spread strategy will always be equal to the difference between the higher strike price (X2) and lower strike price (X1), regardless of how much or in which direction the underlying asset's price moves before expiration.

Choice C is incorrect. As explained above, both statements are accurate descriptions of a box spread strategy in options trading.