n.抱怨者

=complainer.

We bivouacked on the open plain. 我们在开阔的原野上露营。

The problem is quite plain to us. 那问题我们都很明白。

You needn't labor a point that is perfectly plain. 这点很明显，你用不着讲个没完。

His devotion to music is plain to see. 他对音乐的挚爱是显而易见的。

Is the coastal plain good for farming? 沿岸平原适宜耕种吗？

It's plain that he is the criminal. 很明显，他是罪犯。