The shape of a Rubik’s cube is _________.

The cake is () the shape of a heart.

The shape of the ball is a _________.

Sphere, cylinder and cube are ______________ shapes, because they not only have length and breadth, but also depth.

When people make objects, they choose materials carefully because of their __________.

Rubber is _________, so a ball made of rubber is easy to bounce.

Plastic is ______________, so a clear bag made of it can protect the file from being wet.

Glass is _____________, so we can easily see through the window made of glass.

以下化合物中是天然高分子化合物的是（）