C.seated (remain是连系动词,故用形容词seated作表语.remain seated 保持坐着的状态)
2.B.setting up (考查短语devote sth.to doing sth.)
3.A.he explained
he explained at the meeting for his carelessness in his work是定语从句,修饰先行词the reason .
由于其关系代词that在定从中作explained的宾语,故省略了.
4.A.Shall
Shall I do sth.是用来征求对方意见的.