The decision to keep him in hospital for a second night ---

选D
.
underlines 加下划线.
undertake
1.
承担,着手做；同意,答应
348.undertake vt.承担,着手做；同意,答应
...
2.
从事、同意做某事
undertake v.从事、同意做某事
3.
从事,着手；承担
undertake v.从事,着手；承担
outline英音：['autlain]美音：['aut,laɪn]
名词 n.[C]
1.
外形;轮廓[(+of)]
The outline of Italy suggests a boot.
意大利的轮廓像一只靴子.
2.
略图;素描[(+of)]
Make an outline of the scene before you paint.
在上颜料之前先给此景画一个素描.
3.
提纲,概要;要点;草案[(+of)]
These reports give an outline rather than the details.
这些报告只给了一个大纲,而没有提供细节.
及物动词 vt.
1.
画出...的轮廓,画...的略图
Outline a map of North America.
画一幅北美的略图.
2.
概述,略述
He listened as I outlined my reasons.
他听我扼要地叙述了我的理由.
undergo.经历,经受（变化、不快的事等