1.has been away 因为for half an hour是给了一段持续的时间,只有been 可以作为持续的动作.
2.in the bed,on the dest,under the roof,above the ground?不太清楚你想问什么.
3.eg.Is it supposed to be a cake?suppose是动词,supposed是形容词.通常supposed用的多一些.eg.Are you supposed to be there 3 hour ago?假定,应该的意思.
4.宾语补足语.I want to paint it pink.形容词放最后形容前面的名词（名词作宾语）.
5.不定式补足语.I have a lecture to attend.不定式放最后形容前面的名词（名词作宾语）.