You start by running 5 km, move up to a 10 km, then a half marathon.

你先跑5公里，再跑10公里，然后跑半程马拉松。

Three weeks until the half marathon!

距离半马拉松赛不到三个星期了！

Are you running a half marathon this year?

你今年去跑半程马拉松吗？

I am currently training for a half marathon.

我当前正为了半程马拉松进行训练。

Tell everyone that you are running a half marathon!

告诉每个人你将参加半程马拉松！