对于我们未能及时回复您的询问，我们致以诚挚的歉意。

We offer our ___sincere apologies for the delay in responding to your inquiry.

对于您宝贵的指导和支持，请接受我诚挚的感谢。

Please accept my ___sincere gratitude for your invaluable guidance and support.

董事会向所有志愿者的奉献精神表示诚挚的感谢。

The board extends its ___sincere appreciation to all the volunteers for their dedication.