Jim couldn’t understand how the machine worked until his friends how to use it.
A. promised
B. explained
C. thought
D. heard
网友回答
A. promised
(答案→)B. explained
C. thought
D. heard
解析：考查词义辨析。promised 答应，允诺，explained解释，thought认为，heard听到，句意：吉姆不明白这台机器如何工作直到它的朋友们解释了如何使用。所以选B。