Hardly had (a)/ I left the house (b)/than it began(c)/to rain (d)/No error (e) | Sentense error/Grammatical error

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Sentense error/Grammatical error
Hardly had (a)/ I left the house (b)/than it began(c)/to rain (d)/No error (e)
1.(a)
2.(b)
3.(c)
4.(d)
5.(e)
Correct Answer: c [when should be used in place of “then”]