Meaning of 'you sound clear'

[ohnmar]

Test No. incompl/elem-25 "On my Mobile", question 4

You ......... very clear.

(a) sound
(b) ring
(c) hear
(d) noise

Test No. incompl/elem-25 "On my Mobile", answer 4

You sound very clear.

Correct answer: (a) sound

Your answer was: incorrect
You hear very clear.
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what the meaning of sound in here.
can i use hear also?

thanks
ohnmar

[Alan]

You sound clear means the line is good.
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English as a Second Language
You can read my ESL story A day in the life of a parliamentary candidate