But some light passes into the layer and reflects off the bottom surface.

但阳光进入该层并从底部表面反射。

The problem is sometimes, the bottom surface isn't the one you want down.

问题是有时候，底部并不是你想要的。

The upper surface of an airplane's wing is curved, and the bottom surface is flat.

飞机机翼的上表面是弯曲的，而下表面是平坦的。

So one of the things he did was actually use his waffle iron to actually create an outsole which is the bottom surface of the shoe.

所以他所做的其中一件事实际上是用他的华夫饼熨斗来制作一个外底，也就是鞋子的底面。

The oral surfaces covered by non-keratinized stratified squamous epithelium include the buccal mucosa, the floor of the mouth, the lateral and ventral (or bottom) surfaces of the tongue, the soft palate, and the retromolar trigone.

口腔表面由未角化的复层鳞状上皮覆盖的结构，包括颊黏膜、口底、舌的侧面和腹侧（或底面）、软腭与磨牙后三角。