Final answer:
A frame-shift mutation nearly always results in a nonfunctional protein due to the alteration of the reading frame after the mutation, changing the entire amino acid sequence that follows.
Step-by-step explanation:
The mutation that nearly always results in a nonfunctional protein is a D) Frame-shift mutation. A frame-shift mutation is caused by an insertion or deletion of a number of nucleotides that is not a multiple of three, which alters the reading frame of the gene. As a consequence, this changes every amino acid in the protein sequence following the point of the mutation. This severe alteration typically yields a completely nonfunctional protein due to the extensive change in its amino acid sequence. Silent mutations, on the other hand, do not change the amino acid sequence and thus often do not affect protein function. Missense mutations result in a single amino acid change and may or may not impact the protein's functionality, depending on the importance of the altered amino acid. Nonsense mutations introduce a premature stop codon, often leading to a truncated and often nonfunctional protein, but are distinct from frame-shift mutations, which affect a larger portion of the protein.