D-branes are large, massive surfaces that float within space.They act like slippery sheets of flypaper: the ends of open strings move on them but cannot be pulled off.

• 膜是飘浮在空间里具有质量的大型曲面，它们的行为类似滑溜的苍蝇纸：开弦的尾端可在其表面移动，但却无法脱离它。