设$\frac{1}{2}<{\left(\frac{1}{2}\right)}^b<{\left(\frac{1}{2}\right)}^a<1$，那么（）

阅读下面的文字，回答问题。

路边开满了带刺的蔷薇花，三个步行者打这里路过。

第一个脚步匆匆，他什么也没看见。

第二个感慨万千，叹了口气说：“天，花中有刺!”

第三个却眼睛一亮，说：“不，________________________!”

第一个人挺麻木，他看不到风景；第二个人挺悲观，风景对于他没有意义；至于第三个人嘛，他是个乐观主义者。

朋友，你是哪一个呢?

根据短文，选择正确答案。

    This is a picture of a family. The grandmother's name is Harry Smith. The grandfather's name is Jean Smith. They are very old. They are Americans.

    The father'sname is Lake Smith. He is 44. The mother's name is Kate Smith. She is 40. They have a son of ten and a daughter of fifteen.   

    The son's name is John Smith and the daughter's name is Mary Smith. They are students of No.12 Middle School. Kate is a teacher of the same school. Lake is a policeman. It's a very good family.

下列关于生物大分子的结构和功能的叙述中，正确的是（　　）