This is my trousers这里为什么要用is,trousers不是复数吗

This is my trousers这里为什么要用is,trousers不是复数吗 This is my black trousers改错 The trousers are mine还是The trousers is mine?为什么? but there is some in this jug为什么这里用is?some不是复数吗 trousers是复数吗 How much ()the trousers .用is还是are,为什么 This pair of blue trousers is Tom's.The black trousers is To how much IS this pair of trousers ten dollars()enough 老师说用is this pair of block trousers 填is还是are This pair of trousers is 80 yuan.80 yuan提问 What color is your trousers? 为什么underwear不用复数形式,而pants,trousers就要用?