Link please to your claim of that 30x rule else it did not happen. Thanks
The answer is C. The only thing you can do with the account is reduce open positions. You cannot open new positions even if they serve to reduce risk.
IB has instituted a 30x rule that you will find no documentation on. That rule states that, if the sum of the notional value of your option positions exceeds 30x your account mark, you can open no further positions, even if the longs and shorts offset each other (as they do in this case).
In my example, we have longs valued at $4,050,000 and shorts valued at $4m for a total of $8,050,000. Now divide by 30 and we have $268,333.33 which exceeds your account value and locks you down. You can only sell your debit spreads at likely unfavorable prices.