Explanations:In the context of agriculture in Bihar, a food and fodder crop that can be grown both as a Kharif (summer) and Rabi (winter) crop requires specific environmental conditions to thrive. The ideal temperature range for such a crop is 21$^\circ$-27$^\circ$ C, which is moderate and conducive to the growth of the crop during both seasons. This temperature range ensures that the crop can withstand the varying climatic conditions of Bihar, which can be quite diverse between the summer and winter months.
The soil type is also a critical factor in the growth of a food and fodder crop. In Bihar, the soil is predominantly alluvial, which is rich in nutrients and suitable for agriculture. However, the specific type of alluvial soil that is ideal for this crop is old alluvial soil. Old alluvial soil has been deposited over a long period and has had time to develop a rich structure and nutrient content, making it highly suitable for crop cultivation. New alluvial soil, on the other hand, is younger and may not have the same level of nutrient content or soil structure, which can affect the growth and yield of the crop.
The combination of the ideal temperature range and the appropriate soil type is crucial for the successful cultivation of a food and fodder crop in Bihar. The temperature range of 21$^\circ$-27$^\circ$ C ensures that the crop can grow well in both the Kharif and Rabi seasons, while the old alluvial soil provides the necessary nutrients and structure for optimal growth. This combination of factors makes option C the correct answer, as it specifies the ideal conditions for the crop in question.