针对发生在非洲的埃博拉疫情，中国政府自今年4月至10月先后组织实施了3轮援助举措，向13个非洲国家提供了防护救治的物资、粮食食品及现汇援助，派遣了公共卫生专家组和医疗队，提供了生物安全的实验室，向联合国世界卫生组织、非盟等国际和区域组织提供捐款等。这表明（   ）

    Mr. Jackson is a painter. He likes children very much. He always teaches children to paint pictures on weekends.

    Spring is coming Mr. Jackson decided to take children into the garden to paint the beautiful flowers .He took the children to a small garden near the school. The garden was full of spring flowers. Mr. Jackson and children began to paint, but a boy called Andy was just walking around in the garden.

    Two hours later, most of the children finished their pictures. They showed their beautiful pictures to Mr. Jackson. Andy showed his paper to Mr. Jackson, too.

   “What's in the picture?” Mr. Jackson asked angrily. He saw only a piece of white paper .There was nothing on it.

    Andy answered, “I painted some white flowers in the garden and a white bird in the sky.”

根据短文内容，选择正确答案。

洋葱内表皮细胞没有的结构是（　　）