i have just arrived in china为什么加个have

i have just arrived in china为什么加个have I have just arrived in China为什么要加 have I have just arrived in Scotland. 为什么用in那,in不是在什么的里面的意思吗? i have just arrived here 句中arrived 是什么词性 I have just moved to a house in Bridge Street.为什么要加HAVE i have just arrived by train.为什么有have.它起什么作用 Jimmy writes i have just arrived in London 改为间接引语 I have just arrived by train这里为什么要用现在完成时呢 I have just arrived in Scotland.我就一直没明白到底这个have要怎么用,怎么办? I just want to know when you have arrived I have just moved to a house in bridge street.这句话里in 后面为什么不加 在英语上怎样把直接引语改成间接引语如I have just arrived in Scotland