scratch/scrape the surface idiom
仅触及问题的表面
to deal with only a very small part of a subject or a problem
There's far more to be said - I've only had time to scratch the surface in this talk. 要说的还有很多——由于时间关系，这次我只能粗略地谈一下。
The amount of aid that has been offered is hardly going to scratch the surface of the problem. 所提供的救援物资很少，对于解决问题只是杯水车薪。