Meaning of "no dice" and "off the cuff"

[HomerMe]

English Language Tests, Intermediate level

ESL/EFL Test #291 "English Slang Idioms (13)", question 9

His secretary reminded him about the speech, but he had no time to prepare for it. He would just have to give it ......... the cuff.

(a) on
(b) at
(c) from
(d) off

English Language Tests, Intermediate level

ESL/EFL Test #291 "English Slang Idioms (13)", answer 9

His secretary reminded him about the speech, but he had no time to prepare for it. He would just have to give it off the cuff.

Correct answer: (d) off

Your answer was: correct
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Please, explain the meaning of "no dice" and "off the cuff."

[Mister Micawber]

.
no dice" = certainly not
"off the cuff" = unplanned, without preparation
.
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Native English teacher at Mister Micawber's