Where vs. when

[sinus]

English Error, Elementary Level

ESL/EFL Test #15 "The Months of the Year", question 8

Spring starts in March. April the first is known as All Fools' Day where people play practical jokes on each other. In May I'm usually very busy in my garden.

(a) is known
(b) where
(c) busy

English Error, Elementary Level

ESL/EFL Test #15 "The Months of the Year", answer 8

Spring starts in March. April the first is known as All Fools' Day when people play practical jokes on each other. In May I'm usually very busy in my garden.

Correct entry: when
The error was: (b) where
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I don't understand the error!

[Conchita]

When means at what or which time, like April or last year.

Where means at what or which place, like a town or a park.