The first decade of the 21st century the breathtaking and non-stop development of China.

问题补充：

The first decade of the 21st century the breathtaking and non-stop development of China.

A. witnesses

B. witnessed

C. will witness

D. had witnessed

答案：

A. witnesses

(答案→)B. witnessed

C. will witness

D. had witnessed

解析：本题的关键词是句子的主语the first decade of the 21st century指过去的一段时间，做主语的时候谓语动词使用一般过去时。句义：21世纪最初的见证了中国令人窒息的不停顿的发展。故B正确。