根据短文内容判断正误。

    Tom has a strong and faithful dog, Bruce. The dog likes playing with Tom. Sometimes he also follows Tom's father to work.
One morning when Tom's father worked in the field, he took off his coat and put it on the ground under a big tree. He turned to the dog and said,“Watch my coat, Bruce!”
   Bruce sat down on the coat. Later Tom's father remembered he had to buy some food. So he hurried to the shop. After shopping, he went home directly and forgot all about his coat and the dog.
   Late in the evening Tom looked for his dog everywhere in the house, but he couldn't find him. At this time Tom's father suddenly remembered his coat and the dog. He went back to the tree at once. He found that Bruce was still sitting on the coat!

下列划线字注音全都正确的一项是（  ）

原始大气与现在的大气不同，成分中缺少____ ．