Difference between when and who

[Guest]

Test No. errors/elem-14 "Listen and Improve Your English", question 4

We call the person when is listening a listener. We hear with our ears.

(a) call
(b) when
(c) hear

Test No. errors/elem-14 "Listen and Improve Your English", answer 4

We call the person who is listening a listener. We hear with our ears.

Correct entry: who
The error was: (b) when
_________________________

explanation about the correct answer

[Alan]

When is a conjunction of time and who is the relative pronoun.
_________________
English as a Second Language
You can read my ESL story Conditionals