We regret to inform you that there are no tickets for Fridays performance.A. availableB.

问题补充：

We regret to inform you that there are no tickets for Fridays performance.

A. available

B. useful

C. convenient

D. affordable

答案：

(答案→)A. available

B. useful

C. convenient

D. affordable

解析：根据主句中regret一词可体会说话者是语气非常客气地说明了没有星期五演出的票。available“可得到的，存在的”，和句意相符。