做匀速圆周运动的物体，下列哪些量是不变的（   ）

现在一种由碳、氢两种元素组成的有机环状化合物，其结构式简写成下图（4），该物质的名称是____，其化学式是____。

某有机物24g完全燃烧，生成14.4g H₂O和17.92L CO₂（标准状况下），0.5mol此有机物的质量为30g．求：

（1）有机物分子式．

（2）已知此有机物具有弱酸性，能与金属钠反应，也能与碱溶液反应，试写出它可能的结构简式．

    In early spring, the changing temperature usually makes a number of Chinese people uncomfortable. Cold air, bringing rain or even snow, easily tears up(破坏) the warmth of the spring within a night(一夜之间).

    However, with the coming of Guyu-the Grain(谷物) Rain, the blue sky and gentle winds would finally stay. Falling usually on or around April 20 every year, Guyu is the sixth of the 24 solar terms(节气). It means the beginning of a lively summer and people get busy from now on.

    Sow(播种) grains

    This is an important period of the growth of grains. The ancient Chinese already knew that as Guyu comes, the weather will become warm enough for sowing. The farmers usually catch the chance to plant rice, corn and beans.

    Hope for safety and harvest

    For those living near the sea, they will hold some ceremonies(仪式) on Guyu, hoping for safety as well as harvest during the coming fishing season.

    Watch the peony

    It's also a great time to see the peony(牡丹), which is known as “the Queen of All Flowers” in Chinese culture. As a result, watching peonies becomes one of the most enjoyable activities for many. The flower is said to be the favourite of Empress(女皇) Wu Zetian of the Tang Dynasty, who was the only woman ruler in Chinese history.

    Pick tea leaves

    Tea leaves picked before Guyu are among the best tea leaves. People believe that the tea leaves picked on the day of Guyu can make eyes clear and drive away bad luck. So the habit of drinking tea at this time of year has become a tradition in some places of China.