Meaning of "all day long"

[Lola]

Common Errors in English, Advanced Level

ESL/EFL Test #14 "Gerunds and Prepositions", question 5

I'm absolutely sure that that's the man whom has been following me around all day long.

(a) absolutely
(b) that's
(c) whom
(d) all day long

Common Errors in English, Advanced Level

ESL/EFL Test #14 "Gerunds and Prepositions", answer 5

I'm absolutely sure that that's the man who has been following me around all day long.

Correct entry: who
The error was: (c) whom
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what does all day long mean?

Lola

[Mister Micawber]

.
All day long = all day; the entire day
.
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Native English teacher at Mister Micawber's