Abstract: The present invention relates to a multi-component host material and an organic electroluminescent device comprising the same. By comprising a specific combination of the multi-component host compounds, the organic electroluminescent device according to the present invention can provide high luminous efficiency and excellent lifespan characteristics.

Abstract: A rolling boot used in a constant velocity joint includes: a first fastening portion that is configured to be fastened to a joint shaft of the constant velocity joint; a second fastening portion that is configured to be fastened to a joint case of the constant velocity joint; a first folding portion that is configured to be folded when the constant velocity joint is articulated; a second folding portion that is configured to be folded when the constant velocity joint is articulated and is disposed radially outside the first folding portion; a support portion that is configured to support tensile and compression when the first folding portion and the second folding portion are folded; a first peak connecting the first fooling portion and the second folding portion; and a second peak connecting the second folding portion and the support portion.