Answer: B
Correct answer: Image resolution is reduced to make the file smaller
Compress Pictures, on the Picture Format tab, reduces the stored resolution of images to shrink the file. A target resolution is chosen - typically 220 ppi for print, 150 for on-screen use, 96 for email. It matters because photographs from a modern camera are far larger than any slide needs, and a presentation of thirty such images can run to hundreds of megabytes for no visible benefit. The dialogue offers a second and often more significant option: delete cropped areas of pictures. Cropping in PowerPoint only hides the surplus, which remains in the file and can be restored - so a heavily cropped image still carries its full original. Removing those areas can shrink a file dramatically, at the cost of the crop becoming permanent. Compression can be applied to one image or to all of them, and the loss of quality is not undoable once the file is saved. Keeping the originals elsewhere is the sensible precaution.