Which of the following is most likely to cause a gain-of-function mutation?

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A gain-of-function mutation occurs when a protein has increased activity or a new function is acquired. Constitutive activation of an enzyme, such as in the case of a mutation that causes the enzyme to be active all the time, is most likely to cause a gain-of-function mutation. Deletion of a promoter region (A) may decrease or eliminate gene expression, and a null mutation (D) completely eliminates gene function, neither of which would cause a gain-of-function mutation. A synonymous mutation (C) changes a codon but does not affect the resulting protein sequence, so it would not cause a gain-of-function mutation. RNAi (E) is a mechanism for decreasing gene expression and would not cause a gain-of-function mutation.

Which of the Following Is Most Likely to Cause a Gain-Of-Function