In order to solve the problem as soon as possible they had a discussion.A. face-to-face

问题补充：

In order to solve the problem as soon as possible, they had a discussion.

A. face-to-face

B. face to face

C. faces-to-faces

D. faces to faces

答案：

(答案→)A. face-to-face

B. face to face

C. faces-to-faces

D. faces to faces

解析：考查固定短语。face to face相当于副词，修饰动词；face-to-face相当于形容词修饰名词，故答案为A。