I was surprised by the large ________ people who came.

Number of

Amount of

Sum of

None of these

I was surprised by the large number of people who came

میں آنے والے لوگوں کی بڑی تعداد سے حیران تھا

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"The number of" is different and always takes a plural noun followed by a singular verb

the phrase "a large number of" is used to indicate that there were many people who came