7. The curve y = x VI - x is concave downward on the interval A. (-00, 1) B. (-00, 1] C. (3.1) D. (3.1] 8. The points of inflection of the graph of y = sin x + x occur at A. *+2nn, where nel B. " + nx, where nel C. nx, where nel D. "+2nx, where nel Use the following information to answer questions 9 and 10. An open box is constructed from a rectangular sheet of cardboard by cutting out squares from each corner and folding up the sides. The original sheet is 8 cm by 5 cm, and the squares have a side of x cm. 9. The volume I' expressed as a function of x is A. V=4x - 26x2 +40x B. V=4x -13x +40x C. V =2x3-26x2 + 20x D. V =2x -13x3 +20x