terribly,fun,sweet,safe中,哪一个是形容词?

terribly,fun,sweet,safe中,哪一个是形容词? It's terribly cold today.、这里为什么用terribly Grandpa is(terribly)ill and she's in hospital now.为什么是这种词性,terribly Wow、That‘s so sweet、” tastes s( )sugar or sweet that's __ fun sweet sweet Sweet sweet sweet Sweet sweet sweet sweet Sweet sweet sweet