If you wash your skin and hair several times a day,you will soon have dry skin that easily cracks and bleeds because the oils you have removed are necessary to keep the skin supple.This oil is
A)pili secreted by arrectors. B)lymph secreted by lymphatic ducts. C)sebum secreted by sweat glands. D)sebum secreted by sebaceous glands. E)salty sweat secreted by sweat glands.