The right answer is Recombination AND Genetic drift
Recombination is an exchange of genetic information (strand of DNA) between two different sectors of the genome. A frequent example is the meiosis between homologous chromosomes (crossing over).
Genetic drift is the evolution of a population or species caused by random phenomena, impossible to predict. From the genetic point of view, it is the modification of the frequency of an allele, or of a genotype, within a population, independently of the mutations, the natural selection and the migrations. Genetic drift is caused by random and unpredictable phenomena, such as the chance of sperm and egg encounters, in the case of sexual reproduction.