Much to my regret you weren't at home when I called.

奉访未晤,甚怅.

《现代汉英综合大词典》

Much to my regret, I am unable to accept your kind invitation.

不能接受您的盛情邀请,深为抱歉.

《现代汉英综合大词典》

Much to my regret, I refused to accept your kind invitation.

(当时)拒绝您的盛情邀请, 深感后悔.

《现代汉英综合大词典》

Much to my regret, I'm unable to accept your kind invitation.

我不能接受你盛情的邀请,非常遗憾.

《现代英汉综合大词典》

Much to my regret, I must leave you now.

很抱歉, 我现在得走了.

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Much to my regret, I have an important appointment with Mr. Sheila.

很遗憾, 我和席勒先生有个重要的约会.

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Much to my regret that we have made repeated application for payment amount without avail.

我们多次去函请求结清这笔账款而无任何结果,为此我们非常遗憾.

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