《剑桥高阶英汉双解词典》 attention 条的一个例句：
A good teacher is always attentive to their students needs. 一个好的老师一直对学生的需要非常关心。
对于句中的物主代词 their 我不是非常理解。我感觉 A good teacher 应该对应单数物主代司 his，而不应是 复数形式的物主代词 their，请专家指教，谢谢！
你提供的词典例句是正确的，并非笔误。关于这个问题，Michael Swan《牛津英语使用方法指南》有具体说明：
they / them / their 常常用来指单数不确定的人，常常用在 a person, anybody/one, somebody/one, nobody/one, whoever, each, every, either, neither和no后面。在这样的情况下，they用复数动词。
If a person doesnt want to go on living, they are often very difficult to help. 一个人如果不想活下去的话，常常让人爱莫能助。
If anybody calls,take their name and ask them to call again later.假如有人来电话，就把他的名字记下来，同时请他迟些再打电话来。
Nobody was late, were they? 无人迟到吧？
Whoever comes, tell them Im not in. 不管哪个来，告诉他我不在。
......
当所指的人可能是男士也会是女人时（正如上面所举的例子），they / them / their 的这一单数使用方法用起来很便捷。用he or she, him or her 与his or her会非常累赘，特别是在需要重复用的时候。不少人在这状况下不喜欢沿用以前的使用方法，即用he / him / his。
然而，they / them / their 也可以用于性别明确的场所。下面举几个采访中的例子：
I swear more when Im talking to a boy, because Im not afraid of shocking them. 我跟男生谈话，爱说脏话，由于我不怕吓着他们。
No girl should have to wear school uniform, because it makes them look like a sack of potatoes. 女生不肯定非穿校服不可， 由于校服使她们看着像一大口袋土豆。
they / them / their 有时用来指一个具体而又不确定的人。
I had a friend in Paris, and they had to go to hospital for a month. 在巴黎我有一位朋友，他得去医院看一个月的病。
