A plain necklace was her only adornment.

她身上的饰物就只有一串简单的项链。

《牛津词典》

He was attired in a plain, mud-flecked uniform.

他身穿一件朴素而沾有泥点的制服。

《柯林斯英汉双解大词典》

Death valley is this desert plain, a dry lake bed in California surrounded by mountains and on the desert floor these huge rocks, some of them hundreds of pounds.

死亡谷是一片沙漠平原，是加利福尼亚的一个干涸的湖床，四周群山环绕，在沙漠的地面上有巨大的岩石，有些重达数百磅。

youdao

The town lay on a flat plain at the base of an Allegheny Mountain valley so steep that the hillsides rose straight upward along the Little Connemaugh River.

VOA: standard.2010.04.26

Just to be a little bit more plain about that.

说得更明白一点

耶鲁公开课 - 古希腊历史简介课程节选

That area was controlled by Egypt at the purported time of the Exodus Running north to south, next to that coastal plain, is a region of low mountains.

在出埃及记时期，这个地区被埃及所控制,南北分布，靠近海岸平原，是低矮的山区。

耶鲁公开课 - 旧约导论课程节选

What do you make of householders turned austere pilgrims who live in tatty canvas tents on a flood plain of a river braving regular baths in freezing water, biting cold, smoky skies and ear-splitting din for more than a month?

BBC: Does the Kumbh Mela experience improve your well being?

You'd be forgiven for thinking you'd wandered into the wrong venue and taken your seat for a classical piano recital - all that stands before us is a plain stage and a grand piano.

BBC: Review: Rufus Wainwright at the Ipswich Regent, 2010

And I remain impressed that for less than the price of a cup of coffee, I can pop a plain envelope into a box and have confidence, more often than not, that it will be delivered halfway around the world.

FORBES: U.S. Postal Service To Eliminate Saturday Delivery: Will It Save Tax Dollars?