1.l saw her crossing the road yesterday.
翻译是我昨天看见她过马路。
2.The union has written to Detroit seeking clarification on the situation.
翻译是工会已经写信给底特律，要求对此情况给予澄清。
3.they expelled two russians saying they were spies.
他们驱逐了两名俄罗斯人并说他们是间谍。
既然crossing，seeking，saying在这宾补，和宾语是直接关系，那第二三句是不是表达错误，必须得在现在分词前加逗号才行?求解
常见如下动词后可跟现在分词作宾语补足语： see, watch, hear, feel, find, get, keep, notice, observe, listen to, look at, leave, catch等。
例如： Can you hear her singing the song in the next room? 你能听见她在隔壁唱歌吗？
所以第一句可以说是正确的。
第二句话中“要求对此情况给予澄清”是作为目的的，作目的状语常用的是动词不定式，所以这句应该是The union has written to Detroit to seek clarification on the situation.
第三句话中，“saying they were spies.”并不是宾补，发出这个动作的人是they，而不是the Russians，所以“saying they were spies.”是they的后置定语，由于直接放在they的后面会显得句子头重脚轻，所以放在后面了。可以将原句格式理解为：
The policemen，saying the two Russians were spies，expelled them.
所以第三句分词前面必须加逗号对吧
