请问Much -----(我感到遗憾),I was unable to finish the work on time.

请问Much _____(我感到遗憾),I was unable to finish the work on time.
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答案为regret as i felt.但是这题的考点是句型adj.+as+主语+谓语.regert只能做n./v.而形容词是regretful,为什么答案给的还是regret,