What is the difference between 'affect' and 'effect'?

[Oksana]

English Language Tests, Intermediate level

ESL/EFL Test #218 "Confusing Words test (1)", question 1

How much of an ......... did World War II have on Europe?

(a) affect
(b) effect
(c) effects
(d) affects

English Language Tests, Intermediate level

ESL/EFL Test #218 "Confusing Words test (1)", answer 1

How much of an effect did World War II have on Europe?

Correct answer: (b) effect

Your answer was: incorrect
How much of an affect did World War II have on Europe?
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What is the difference between 'affect' and 'effect'?

Thanks

[Mister Micawber]

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AFFECT vs EFFECT.
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Native English teacher at Mister Micawber's