Question

Karan________continuously.(smoke)

Answer 1

The answer to this uses present tense so it's
Karan SMOKES continuously 

Answer 2

Heya !!!

Here is your answer,

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Karan ____ continuously. (smoke)

"Karan" is a singular,
So we will use singular form of "smoke".

Singular form of "smoke" = 'smokes'.

Ans. Karan smokes continuously.

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Hope it helps.