Final answer:
Sieve tube is not a part of the flower. The anther is the correct structure where pollen grains develop, which is part of the stamen, the male reproductive organ of a flower.
Step-by-step explanation:
Among the options given, sieve tube is not a part of the flower. Flowers consist of four primary structures: sepals, petals, stamens (male reproductive organs), and carpels (female reproductive organs). Sepals form the outer layer of the flower, often resembling leaves and collectively called the calyx. They protect the developing flower bud. Petals, which make up the corolla, are typically colorful and attract pollinators. The stamen is made up of the filament and the anther, where the pollen grains develop. The carpel, or pistil, includes the sticky stigma that receives pollen, the style, and the ovary that houses the eggs.
The correct answer to the student's question about where pollen grains develop is "a. the anther". Pollen formation occurs in the anthers of stamens, which are the male reproductive structures of the flower.