PET饮料瓶的瓶口怎么是白色的

白色是由于冷却问题造成的，白色是结晶度高的原因，两种PET加工的温度是有很大区别的。

A pet is all animal which is raised or kept by people as a companion. In recent years, more and more people, old or young, rich or poor, like to keep a pet such as a dog, a cat, a monkey and so on.
But pets are sometimes trouble-makers. Some pets such as dogs or snakes may attack people unexpectedly. A lot of people become ill or get infected because of the virus carried hy their pets. And some pets are dirty and poisonous. Therefore, we do not advocate keeping pets.
My grandmother gave me a cat as a birthday present. It was named Mini. It was black and white. When I came back home,she usually ran to me and played with me. When I was doing my homework, she used to lie under the table quietly. She loved to look at herself in the mirror. She kept clean and enjoyed being washed. She was such a nice and lovely cat. A week ago when I took her out, she was so happy running around. Unfortunately she was lost. Since then I have ne