going out for dinner this evening?

答案：D
1、let's,why not,shall we 后面都是接动词原形,所以排除ABC.
2、How about = What about 表示“...怎么样”,about是介词,后面动词的ing形式,所以正确答案是D.
翻译：今天晚上去外面吃饭怎么样?