不知道是性别, 用哪个代词?

讲解内容见语音, 例句....

1)  I got a strange call from someone last night. What did they say?  我昨天晚上接到了个很奇怪的电话? 她/他说什么了?

2) There's a new employee starting today, but I haven't met them yet. 今天有个新员工来, 但是我还没见到他/她呢.

3) I heard you made a new friend at the party. What's their name? 我听说你在派对上交了个新朋友, 她/他叫啥名啊?