1.Have you seen my dictionary?I can't find it anywhere

1.Have you seen my dictionary?I can't find it anywhere
I_____it on the shelf when I came in
空为什么填saw而不能填have seen
2.Lucy used to be afraid of scary(scare) snakes
为什么是scary scaring貌似也说得通
3.Grandpa is sitting comfortably(comfortable) in the sofa
求解这里为什么接一个副词 形容词不行吗?
4.They thought____impossible to finish the work by 8 o'clock in the evening
A that B which C it D it's
求解释为什么选C不选别的