Being often used as pain-killer can give rise to the__________belief that cocaine is not an addictive drug. [ ]

I can’t find Xiao Ping. Where did you see him this morning?— In the reading room _________ he often studies in.

Without the mobile phone and Internet，communicating with each other ________ quite difficult today.[ ]

It’s better to express your anger ______ bottle it up.

What about my model boat — It’s one I have ever seen.