Multiplexer [closed]

Question

what is the Minimum number of 21 multiplexers required to realize the following function 

Assume that inputs are available only in true and Boolean constants 1 and 0 are available.

 

Shouldn't the answer be 1 ??

Comments

is it 3 ??

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it is 2

Answer 1

why do you think it's one? I think it's two!

https://drive.google.com/open?id=0B-gSRvFBWKyDaEl0eDF4Qk9rMTNadXhUNGowN1kyXzZqOXIw