why we can ear the roar of sea on holding a sea shell to your ear?

Question

i have five options, please select the right one:

a) the shell comes from the sea

b)because of hallucination

c)the shell is hollow

d) the effect of multi reflections of air produces a vibrating sound

e) none of these

all may appear to be correct!! but please choose me the right one.
this question was asked on a assignment, but i couldn't find it out. please tell me thecorrect answer with GOOD EXPLANATION. i hope you will do this. if you did so, i will select you as the best answerer.

Answer 1

I always thought that it was an echo of the blood rushing in the middle ear.

Anyway look here for the correct answer ... I bet you nobody really knows.

http://science.howstuffworks.com/question556.htm

Answer 2

first off, a, b, and e are all wrong. C and D are partially correct, however I think D is the right answer. The shell is hollow, therefore allowing air to pass through and bounce off the sides (or reflect off them), which produces the sound you hear

Answer 3

the "road" you can hear when holding a shell to your ear, is the echo, or rather the multiple echoes, of arterial blood pumping in and around your ear.

so (c) is valid (though only part of the explanation). And (d) is valid also.

but none of your choices include anything relating to the real cause, ie blood flow.

Answer 4

Antoine Bachmann is very right.
I can only add that if you cup your palm tightly on your ear - you can hear similar sounds.