sum vs amount

[Goran]

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #72 "At the End of the Day (1)", question 3

but whatever the required ........., all of us need sleep at some time during the day or night.

(a) sum
(b) total
(c) amount
(d) lot

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #72 "At the End of the Day (1)", answer 3

but whatever the required amount, all of us need sleep at some time during the day or night.

Correct answer: (c) amount
_________________________

is this correct?

Goran

[Kitosdad]

At the end of the day

again, sum would appear to be apt in this situation .,
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Englishman living in Germany.