二十四节气是中国农耕文明的宝贵遗产。即使中国古代有着自己的授时系统，但古代的人民群众在一定程度上仍依靠二十四节气指导生产和生活。不可否认的是，少数地方的节气传统正在消减，年轻人对节气的认知逐渐淡薄，由于近年来城市化进程过快，这直接弱化了二十四节气的各种功能。二十四节气申遗成功后，我们只要加大宣传力度就能做好传承和保护工作。
①假设关系不成立，应当修改为：虽然中国古代有着自己的授时系统。
②____，应当修改为：这进一步弱化了二十四节气的各种功能。
③条件关系不成立，应当修改为：____。
速度是表示____ 的物理量，它的国际主单位是____ （填单位名称和符号）
A
Most Americans start to school at the age of five when they enter kindergarten(幼儿园). Children do not really study at this time. They only attend for half the day and learn what school is like. Children attend elementary school for the next six years. They learn to read and write and work with numbers. They also study the world and its people. After they leave elementary school, children go to junior high school for three years and senior high school for another three years. This is called secondary education. In some places, the children go to elementary school for eight years and high school for four. In all, elementary and secondary education together take twelve years to complete excluding （不包括）kindergarten.
根据短文，选择最恰当的选项。
