The correct answer is: A. sales value at split off method.
The sales value at split off method is a joint cost allocation method that allocates joint costs to joint products based on the relative sales value of the products at the split off point. This method is based on the assumption that the products have different market values at the split off point and that the joint costs should be allocated in a way that reflects these different values.
The other options are incorrect because they do not reflect the relative sales value of the products at the split off point. Option B, joint costs at split off point method, allocates joint costs based on the relative physical quantities of the products produced. Option C, joint products value at split off method, allocates joint costs based on the relative sales value of the products at the split off point, but it does not take into account the physical quantities of the products produced. Option D, main product cost at split off method, allocates all of the joint costs to the main product and none of the joint costs to the by-products.
The sales value at split off method is a simple and easy-to-use method of allocating joint costs. However, it is important to note that this method does not take into account the costs of further processing the joint products after the split off point. As a result, the sales value at split off method may not be the most accurate method of allocating joint costs.