问题
选择题
Jim couldn’t understand how the machine worked until his friends____ how to use it.
A．promised
B．explained
C．thought
D．heard
答案
答案：B
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。