We take this opportunity to express our sincere of your timely help.
A. anxiety
B. ambition
C. association
D. appreciation
网友回答
A. anxiety
B. ambition
C. association
(答案→)D. appreciation
解析：句意，我们利用这次机会，对于你及时的帮助，表达我们真诚的感谢。Anxiety焦虑 ambition抱负 association联合 appreciation感谢，根据题意，故选D。