Claire: As you all know, almost everything can be delivered in Seoul, and I love that! Even hamburgers can be delivered here.

Fangjin: And the speed of delivery is unbelievable. Last night, I ordered fried chicken, and it was delivered in less than 30 minutes. So quick!
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In the last sentence, what is the full form of 'So quick'? (tense...etc)

1. It was so quick!
2. It is so quick!
3. The delivery was/is so quick!
4. The speed was/is so quick!

All four of the answers work, but #3 is the best.

In the last sentence, "So quick!" is a short form or abbreviation of the full sentence "The delivery was so quick!" or "The speed was so quick!" The full form of "So quick!" is implied and omitted in the conversation to express excitement or emphasis. Both options 3 ("The delivery was so quick!") and 4 ("The speed was so quick!") would be grammatically correct depending on the context.