The correct answer is A. oven drying method.
The oven drying method is the most accurate and reliable method for determining the water content of a soil mass. It is also the most time-consuming method. The sand bath method is a quick and easy method, but it is not as accurate as the oven drying method. The alcohol method is a quick and easy method, but it is not as accurate as the oven drying method or the sand bath method. The calcium carbide method is a quick and easy method, but it is not as accurate as the oven drying method, the sand bath method, or the alcohol method.
The oven drying method is the most accurate and reliable method for determining the water content of a soil mass because it removes all of the water from the soil. The sand bath method is a quick and easy method, but it is not as accurate as the oven drying method because it does not remove all of the water from the soil. The alcohol method is a quick and easy method, but it is not as accurate as the oven drying method or the sand bath method because it does not remove all of the water from the soil. The calcium carbide method is a quick and easy method, but it is not as accurate as the oven drying method, the sand bath method, or the alcohol method because it does not remove all of the water from the soil.
The oven drying method is the best method for proper field control because it is the most accurate and reliable method. It is also the most time-consuming method, but it is worth the time to get an accurate reading of the water content of a soil mass.