The swimming pool is open when the high temperature is higher than 20^\circ\text{C}20 ∘
C20, degrees, start text, C, end text. Lainey tried to swim on Monday and Thursday (which was 333 days later). The pool was open on Monday, but it was closed on Thursday. The high temperature was 30^\circ\text{C}30
∘
C30, degrees, start text, C, end text on Monday, but decreased at a constant rate in the next 333 days.

Determine whether the following statements are true and give an explanation or counterexample. bold a. when using the shell method, the axis of the cylindrical shells is parallel to the axis of revolution. bold b. if a region is revolved about the y-axis, then the shell method must be used. bold c. if a region is revolved about the x-axis, then in principle it is possible to use the disk/washer method and integrate with respect to x or the shell method and integrate with respect to y.