阅读理解
A
Mrs. Gill lived next door to Nita. Every afternoon, Mrs. Gill took a walk. She said it kept her young. Nita liked to talk with Mrs. Gill when Mrs. Gill came back. Mrs. Gill was always happy after her walk. She often showed Nita something she had found, like a beautiful red leaf (叶子)
One afternoon, Mrs. Gill looked upset. Nita asked her why.
“I am sad about all the trash (垃圾) on the street,” she said. “I never saw so much trash in this neighborhood! What happened?”
“Mrs. Trent moved,” said Nita. “She used to go out each morning and pick up trash. I often saw her on my way to school.”
Mrs. Gill looked very ▲ . “I thought I knew everything about this neighborhood!” she said. “But you see more than I do!”
“Well, I wish I could do Mrs.Trent's job. But you know, my back (背) often hurts. It's really hard for me to pick things up,” she added.
“I could do that,” said Nita.
Mrs. Gill said, “I will carry the trash bag! You can use my gloves (手套) so your hands can stay clean.”
Nita put on the gloves. She picked up pieces of paper. She picked up boxes. And Mrs. Gill carried the bag. Lots of people stopped to thank Mrs. Gill and Nita. The street looked much better.
“Thanks, Nita,” said Mrs. Gill. “Let's call ourselves the clean-up team!”
根据材料内容选择最佳答案。
，
称为取整函数或高斯函数，亦即
。在直角坐标平面内，若
满足
，则 
的范围是（ ）