If you want to look around ,try the Londin street pavement for the best value and for the best show in town-Londoners go

If you want to look around ,try the Londin street pavement for the best value and for the best show in town-Londoners going about their daily business.这个句子中-Londoners going about their daily business做什么成分,为什么用going about而不用is going about