Every Human Has a Complete Set of Human Genes, but Each

Every human has a complete set of human genes, but each set is unique (except in the case of identical twins) . How can this be?

A) There are typically many different alleles for each gene, so everyone has a unique combination of alleles.
B) There are typically mutations in genes from one generation to the next, so each generation's genes are unique.
C) There are typically many different genes for each allele, so everyone has a unique combination of genes.
D) Because of sexual reproduction, we get alleles from both our parents and they're always different.
E) When our cells divide as we develop as embryos, the alleles we have get shuffled so we all have a unique set.