The glass blocks covering the walls and roof allow natural light to illuminate the entries and extend below-grade through the diagonal space of the stairs and escalators.

玻璃块覆盖的墙壁和屋顶可以让光线照射进来并且向下延伸，通过楼梯和自动扶梯实现对角空间效果。

youdao

The year passed quickly and Ronny had made some progress but he was still below the level of grade.

一年很快过去了，罗尼取得了一些进步，但他的成绩仍然低于正常水平。

youdao

I am one grade below him.

我比他低一年级。

《新英汉大辞典》

All improvements, whether on Vanderbilt or on the below-grade subway platforms, is quite innovative.

WSJ: Not Visionary Enough | By Julie V. Iovine

Corporate bonds rated BBB are yielding 8%, while their below-investment-grade BB brethren yield 9%.

FORBES: Magazine Article

The risk premium in financial markets comes in as Treasury yields move up and fewer below-investment-grade debentures stop trading like yesterday's sardines.

FORBES: Uncle Sam: Not Too Big To Fail