The difference of sample means of two populations is 55.4, and the standard deviation of the difference of sample means is 28.1. Which statement is true if we are testing the null hypothesis at the 95% confidence level? A. The difference of the two means is significant, so the null hypothesis must be rejected. B. The difference of the two means is significant, so the null hypothesis must be accepted. C. The difference of the two means is not significant, so the null hypothesis must be rejected. D. The difference of the two means is not significant, so the null hypothesis must be accepted.

For every corresponding pair of cross sections, the area of the cross section of a sphere with radius r is equal to the area of the cross section of a cylinder with radius and height 2r minus the volume of two cones, each with a radius and height of r. a cross section of the sphere is and a cross section of the cylinder minus the cones, taken parallel to the base of cylinder, is the volume of the cylinder with radius r and height 2r is and the volume of each cone with radius r and height r is 1/3 pie r^3. so the volume of the cylinder minus the two cones is therefore, the volume of the cylinder is 4/3pie r^3 by cavalieri's principle. (fill in options are: r/2- r- 2r- an annulus- a circle -1/3pier^3- 2/3pier^3- 4/3pier^3- 5/3pier^3- 2pier^3- 4pier^3)