Please now dispatch the first part of the order (items 1-8) by air, as these are urgently required by customers. Explanation: The word "urgently" best fits the context here. It suggests that the items are needed immediately or with great haste, which aligns with the fact that they are being sent by air to expedite the delivery. The other options don't quite capture the sense of immediacy and necessity that "urgently" does. "Quickly" is more general and doesn't convey the sense of emergency, "possibly" is not suitable because it means "maybe" or "perhaps" which doesn't fit the situation, and "mostly" suggests a majority rather than an urgent need.
