[观察例句]
观察下列句子并指出黑体部分的语法作用
①My feeling is that they're going to be big one day.
②The question is whether she will offer to help me.
③China is no longer what it used to be.
④This is what makes them so special.
⑤A simple restaurant was where he usually had the same meal of sausages，eggs and coffee.
⑥From space，the earth looks blue.This is because about seventyone percent of its surface is covered by water.
⑦It seemed as if/though the world were coming to an end!
⑧The reason why I'm calling you is that I want to invite you to my birthday party.
