Upon reading the notice all the staff of the company stood there, lookingat each other. A.

Upon reading the notice all the staff of the company stood there , looking at each other. A. no speakingB. speechlesslyC. speechless;D. did not speaking

speechlessly（adv）不是修饰动词stood 的，而是 speechless（adj）用来修饰主语all the staff of the company，即形容词做主补,所以选 C。

谢谢了