Answer:
А . heterogeneous mixture
Explanation:
A heterogeneous mixture is defined as the non-uniform mixture of two or more substances and can be easily separated. Two or more solids mixed together is an example of a heterogeneous mixture.
In the given example three solids: flour, sugar, and baking soda is present in the beaker is non-uniform constituents and represents a heterogeneous mixture as the contents are mixed together but they are still in the solid form.
Hence, the correct answer is "А . heterogeneous mixture".