答案：C

解析：

Suppose that x quarts of the final mixture of dye will be made. Since it is to be made from equal amounts of orange and green dye, it will consist of (1/2)x quarts of orange dye and (1/2)x quarts of green dye. Since the orange dye has 2 parts yellow dye for each 5 parts total dye, 2/5 of it is yellow dye. Similarly, 1/3 of the green dye is yellow dye. The amount of yellow in the final mixture is given by

((2/5)(1/2)x) + ((1/3)(1/2)x) = ((1/5)x ) + ((1/6)x)

= (11/30)x quarts

So 11/30 of the final mixture is yellow dye.

Note: Although "quartsh" were used to express the amount of the final mixture, it could have been pints or any other unit of liquid measure.