表示因果关系时用so或because .例; The box is too heavy ,so I can't move it.这箱子太重了,所以我搬不动它.I can't move the box ,because it's too heavy.我搬不动这个箱子,因为它太重了.
表示转折关系时用but或however.但 however前后都要用逗号隔开,but前面要用逗号隔开 .表示并列 关系时用and 例:I like apples and bananas .我喜欢苹果和香蕉 句子未说完时用 逗号 ,说完时用 句号.