The correct option is C Pollen grains
Haploid plants are useful in plant breeding. Haploids can be used to generate genetic homozygotes by one generation doubling of chromosomes using colchicine. Colchicine prevents spindle formation. Hence, the chromosome number can be easily doubled using colchicine. Anther culture is done for production of haploids because anthers contain haploid microspores (pollen grains) which can be used to generate new plants.