我帮助他上马。

I helped him ___mount the horse.

仅仅走了一小段路后，他就不得不帮助他们中的两个人上骡子。

After only a short walk, he had to help two of them to ___mount the mules.

骑师在比赛开始前迅速上马。

The jockey quickly ___mounts the horse before the race starts.