高考题中的这个句子不能加定冠词，因为这里是表示“登上舞台”：

He goes on stage beside pianist Maria Raspopova. 他与钢琴家玛丽亚·拉斯波波娃一起登上舞台。

go on stage 和 go on the stage 都可以说，但意思不同：

1. go on stage=登上舞台

I went on stage and did my show. 我上台作了表演。

I had an attack of nerves just before I went on stage. 登台前那一刻我感到非常紧张。

Every actor ought to know his lines backwards before he goes on stage. 每一位演员在登台之前都必须背熟台词。

Before she went on stage her chest felt tight and her throat hurt. 她上台前胸口发闷，喉咙疼痛。

Before going on stage, I breathe deeply and think positive thoughts. 在走上舞台之前，我做着深呼吸，头脑里想种种自信的念头。

2. go on the stage=当演员(= to be / become an actor)

She went on the stage (=became an actor) at age 15. 她15 多开始演艺生涯。

He went on the stage shortly after he left high school. 他中学一毕业就当了演员。

Since she was a schoolgirl she had dreamed of going on the stage. 自从上学以来她就一直梦想着成为演员。