How can one protect the stem-end of radish root from becoming green?

Answer: Option B

One can protect the stem-end of radish root from becoming green by earthing.
The most frequent cause of radishes growing only greens is hot weather. Once the weather warms up, the radish plant bolts and tries to set seed. The lack of development is caused by planting too thickly and not thinning about 1 to 2 inches between plants.
In radish, the growing roots tend to push out of the soil surface. Therefore, earthing up and weeding during the early stages of growth is necessary for the proper development of quality roots.