As an additional safeguard against weeds you can always use an underlay of heavy duty polyethylene.

作为另外一种预防杂草的防护措施，你可以一直使用一层厚重耐磨的聚乙烯底垫。

For the next research work well theory underlay.

为下一步研究工作做好理论铺垫。

Are blended with vector graphics, including other video, above (overlay) or behind (underlay)?

与矢量图形混合，包含其它视频，在之上(覆盖)或在后面(衬底)？

With a normal black biro I have drawn this on marker paper, using a photo as an underlay.

首先我用一只普通的圆珠笔在背景层上画上车的大概轮廓。

You can get just a simple plastic underlay sheet and that would provide adequate protection.

你可以只要简单地将塑料垫板、提供足够的保护。