Néng dédào nín de bāngzhù, wǒ gǎndào mòdà de gǎnjī.
I feel immense gratitude for your help.
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Formal/literary. 莫 is classical Chinese for 'none' - so 莫大 literally means 'none greater.' Used in formal speech and writing, rarely in casual conversation.
grammar
Always followed by 的 + noun: 莫大的荣幸 (greatest honor), 莫大的帮助 (immense help), 莫大的鼓励 (tremendous encouragement). Cannot be used as a standalone predicate.
