That or which? (Such is human nature, that a great many people are often...)

[Infin1ty]

Hi,

I read an article entitled 'The double life of Alfred Bloggs' in a book named <<New concept English3>>, which was written by
L. G. Alexander. In this article, he wrote:
Such is human nature, that(is??) a great many people are often willing to sacrifice higher pay for the privilege of becoming white-collar workes.

My questions are: Can the relitive pronoun 'that' be used after a comma? Could I say 'which(is??) a great many people...'? Many thanks.
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Please feel free to correct me if you find any mistakes in my posts.

[Mister Micawber]

.
I think what is intended is simply 'such is human nature that a great many..'-- i.e. the correlative subordinator, 'such...that'. I wouldn't have used a comma, and I consider the comma incorrect there, but perhaps the pause was inserted so that we pause and think a moment.
.
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Native English teacher at Mister Micawber's

[Infin1ty]

Thank you for your kind help again, Mister Micawber.
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Please feel free to correct me if you find any mistakes in my posts.