Their cheerful voices showed that they were having a discussion.A. noisyB. friendlyC. seri

问题补充：

Their cheerful voices showed that they were having a discussion.

A. noisy

B. friendly

C. serious

D. nervous

答案：

A. noisy

(答案→)B. friendly

C. serious

D. nervous

解析：考察形容词词义辨析。A吵闹的；B友好的；C严重的；D紧张的；句意：他们快乐的声音说明他们正在进行一次友好的讨论。根据句意说明B正确。