Foreigners often make some strange mistakes in Chinese when they study the most difficult language— —Chinese. We try to analyze typical sentences to correct these errors.
Tāmen shàngkè, wǒ zǒujìn jiàoshì lái le.
False: 他们上课，我走进教室来了。
Tāmen shàngkè de shíhòu, wǒ zǒujìn jiàoshì lái le.
True: 他们上课的时候，我走进教室来了。
句子的原意是，“我走进教室来了”发生在“他们上课”这段时间里。在汉语里应把主谓词组“他们上课”用在“……的时候”的前边，作时间状语。
The sentence means that "my coming into the classroom occurred during the time they were having class". To express such meaning in Chinese, a subject-predicate phrase such 他们上课 should be used with 的时候 after it, together serving as the adverbial adjunct of time.
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