train (n.)
火车  

例句：
Traveling by train is very convenient in Europe.
在欧洲用火车来旅游是非常方便的。 

be at a premium
需求量很大；奇缺

例句：
Tickets for the football match were at a premium.
那场足球赛的门票需求量很大，很难搞到手。

I'm working on it.
我正在努力。 

对话：
A: Albert, do you drive? 
B: No, but I'm working on it.

A：Albert，你会开车吗？ 
B：不会。我正在学。