however与but的连接作用的分别(急)

however与but的连接作用的分别(急)
这样的两个句子对吗?
Most of the class went on the trip;however,liu Hua stayed at school.
Most of the class went on the trip but Liu Hua stayed at school.
第一个句子的however两边的标点到底应该是什么?
还有这样的话对吗?(but既可以连接两个句子又可以连接句子中的两个并列的成分,however却只能连接两个句子)
还有的说however不能连接两个分句,必须令起新句,用逗号隔开.
这又是怎么回事?
The report shows that we are making progress but that we need to make greater efforts.
这句话的but用法难道不对吗?需要给but 前面加逗号吗?
(只有你不懂我)