sentences:  For case 2, the number of 0-valued bits in the information section have stayed the same, but the value of the check data has changed.Since we know some 1s turned into 0s, but no 0s have turned into 1s (that's how we defined the error model in this case), the encoded binary value of the check data will go down (e.g., from binary 1011 to 1010, or to 1001, or 0011).Since the information data has stayed the same, it has the same number of zeros it did before, and that will no longer match the mutated check value.