下列句子中不是命题的是（      ）

材料一：

材料二： “小时侯，乡愁是一枚小小的邮票，我在这头，母亲在那头……而现在，乡愁是一湾浅浅的海湾，我在这头，大陆在那头。”

——《乡愁》余光中(台湾) 1972年作

材料三：2017年5月21日，台湾著名作家林清玄应邀在山西太原举办讲座。期间林清玄表示，双方经常往来，就会彼此了解、肯定，大陆和台湾的民间交流不可阻挡。目前，甘肃省有300多家台资企业，包括台商投资建设的兰州正林农垦食品有限公司，这家企业主要加工瓜子，年营业总额近5亿元人民币，已成为甘肃省特色农产品加工的龙头企业。

材料四：2016年5月20日，台湾当局新领导人蔡英文发表“5.20讲话”，虽然提及要继续推动两岸关系和平发展，但对“九二共识”的核心意涵回避，对两岸关系根本性质态度模糊。在必须明确接受和平发展的政治基础这道必答题面前，她交出了一份没有完成的答案。

——摘自《人民日报》

请回答：

1948年4月30日，中共中央在纪念“五一”国际劳动节活动中倡议：“各民主党派、各人民团体、各社会贤达迅速召开政治协商会议，讨论并实现召集人民代表大会，成立民主联合政府。”其目的是（    ）

    In Chinese culture, people believe some numbers are lucky or unlucky. This is to see what Chinese character the number sounds like. For example, the Chinese word for the number 8 sounds like the word for “making a fortune”. So, people think it is a very lucky number. Some people spend a lot of money to have 8s in their phone numbers. The opening time of the Beijing Olympics began at 8:08 p.m. on August 8, 2008.

    The number 9 is also a lucky number. It is something to do with the emperors of China. There were nine dragons on emperors' robes(龙袍). Today, 9 often stands for “long lasting”. That's why close friends always use 99 or 999 to describe their friendship.

    So what's a “bad luck” number in China? It might be 4. Many Chinese people see 4 as a “bad luck” number. Because it sounds like the Chinese character for “death”.

    Because of this, many buildings don't have the fourth floor, and just call it the fifth floor. In Hong Kong, some buildings even don't have all floors numbered with 4, such as, 4、14、24、34 and all 40-49 floors. Some buildings also don't have the 13^th floor as 13 is an unlucky number in the West. Now a question for you: How many floors are actually there if a building's highest floor is numbered 50?