virtual gate(huffman coding) [closed]

Question

We use Huffman's algorithm to obtain an encoding of alphabet {a, b, c} with frequencies fa, fb, fc. Which of the following codes cannot possibly be obtained (no matter what the frequencies are)
Code 1 = {0, 10, 11}
Code 2 = {0, 1, 00}
Code 3 = {10, 01, 00}

(A) Only code 2
(B) Only code 2 and code 3
(C) Only code 1 and code 3
(D) None

answer given -(B)

why code 3 is incorrect??

Comments

May be because while constructing tree 

at level-2 we have 3 nodes but we should have even number to merge.

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according to this approach what about option (a)??? can you provide some reference.

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This is a valid Huffman code