“Sceptical” or “skeptical”?

Which is correct?
Responding to rumors that attackers were planning a massive cyber attack, security experts remained ________ of the potential of such an attack to cripple the Internet.
a. skeptical
b. sceptical

Explanation:
“Skeptical” and “sceptical” are both correct but the first spelling is standard in the United States and the second is standard in the United Kingdom.

Grammarist provides examples from various countries.

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