Question

A number of monkeys Sterrounded us. grammatical correction
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Answer 1

Answer:

group instead of number should be there

Explanation:

Answer 2

A troop of monkeys surrounded us.

While we are referring to a collection of things , we use collective nouns. In case of monkeys we use the collective noun 'Troop'. Some more examples of collective nouns are- A brood of Hens, A litter of cubs,  A cast of actors , A group of islands etc. Although , some collective nouns does not specifically refer to one kind of thing, like the word 'group', which can be applied to living things and non-living thingws as well.