用所给词的适当形式填空

1. Tony didn't find __________(learn) English easy.

2. If you keep __________(study) hard, you'll catch up the other students.

3. At different __________(time) of the day, the colours of the rock change from purple to red.

4. The hill is 348 __________(metre) high.

5. The ancient stories always describe the spirits that __________(create) the world.

可塑成型分哪几种？试比较各自特点？