The correct answer is A. Haploids.
Haploids are organisms that have one set of chromosomes, while diploids have two sets of chromosomes. Tetraploids have four sets of chromosomes, and polyploids have more than two sets of chromosomes.
Haploids are the most suitable for the study of mutations because they are easier to manipulate than diploids or polyploids. Haploids can be produced by crossing two different strains of a species, or by treating a diploid cell with a chemical that causes it to lose one of its sets of chromosomes.
Once a haploid has been produced, it can be exposed to mutagens, which are agents that can cause mutations. The mutations that occur in haploid cells can then be studied to determine their effects on the organism.
Haploids are also useful for studying the function of genes. Because haploid cells have only one copy of each gene, any mutation that occurs in a gene will be expressed in the phenotype of the organism. This makes it easier to identify the function of a gene by studying the effects of mutations in that gene.
In conclusion, haploid organisms are the most suitable for the study of mutations because they are easier to manipulate and study than diploid or polyploid organisms.