Write an iterated integral for a. vertical cross-sections, b. horizontal cross-sections. O A. S S a. Write the correct iterated integral using vertical cross-sections. Select the correct answer below and fill in the answer boxes to complete your choice. dx dy OB. S dy dx OA. ffdA dA over the region R described to the right using R b. Write the correct iterated integral using horizontal cross-sections. Select the correct answer below and fill in the answer boxes to complete your choice. [10 dx dy OB. S S dy CHE dy dx 3 y=x R y = 27