He left----any of his friends seeing him off.A:with B:withou

B
without
[wiT5aut]
prep.
没有,不,(表条件)如果没有,要没有
adv.
在外,在屋外
without
with.out
AHD:[w¹Y-out“,w¹th-]
D.J.[wiH6aut,wiG-]
K.K.[w!H6a&t,w!G-]
adv.（副词）
On the outside:
在外部：
a sturdy structure within and without.
内外都很坚固的结构
With something absent or lacking:
缺少：在没有或缺少…的情况下：
had to do without.
没有只好作罢
prep.Abbr.w/o（介词）缩写 w/o
Not having; lacking:
没有；缺少：
a family without a car.
没有汽车的家庭
Not accompanied by; in the absence of:
没有陪伴；没有…：
volunteered without hesitation; spoke without thinking.
毫不犹豫地自告奋勇；脱口而出
At,on,to,or toward the outside or exterior of:
在外面；对着外面；向着外部：
standing without the door.
站在门外
conj.Regional （连接词）【区域的】
Unless:
除非,如果不：
“You don't know about me without you have read a book by the name of The Adventures of Tom Sawyer ” (Mark Twain)
“如果你没有读过一本叫汤姆·索亚历险记 的书的话,你就不知道我” (马克·吐温)