Mutations are defined as changes in chemical structure of gene at molecular level. Since genes are unit of heredity, mutations in genes are passed from one generation to next, exception is lethal mutation; option A is correct and B is incorrect. Owing to genetic code redundancy and diploidy, some mutations are neutral. As we know that wobble base pairing allows multiple codons, most of which differ in ir base, to code for single amino acid. For example, serine is encoded by UCC, UCA, UCG, AGU, and AGC. Therefore, any mutation that changes last letter of codon of serine will have no effect. Diploids have two copies of a gene, presence of one functional copy is sufficient to ignore effects of mutation in second copy. Some mutation is deleterious and provides  raw material for natural selection to act upon and thus causing evolution; option D is correct. Only a few mutations are beneficial that impart survival or reproductive advantage; for example ability of milk digestion in human kids, option C is incorrect. The correct answer is A.