1.Aer these your trousers?（这些裤子是你的吗?）
Aer应该是Are吧
做否定回答是：No,They aren't.(全句应是No,They aren't my trousers)
2.The blue notebook is nine yuan.（这本笔记本9元）
改为否定句是：The blue notebook isn't nine yuan.
祝学习进步O(∩_∩)O