问题补充：
Officials from China and France formally promised on Thursday to build a new type of economic partnership, while business cooperation.
A. strengthened
B. to strengthen
C. strengthening
D. strengthen
答案：
A. strengthened
B. to strengthen
(答案→)C. strengthening
D. strengthen
解析：句意：来自中国和法国的官员在星期四正式许诺在加强商业活动的同时构建新型的经济伙伴关系。这里使用了时间状语从句的省略式，完整的句子是while they are strengthening business cooperation.当主从句的主语一致的时候，可以省略从句的主语和be动词，所以选C。
