下列句子中各有一处错误,找出并该处
1.I have bought the piano for six years._____
2.Where have you gone?I've gone to school _____
3.How many pages have you read by the end of last year?_____
4.While I walked in the street,I saw my teacher._____
5.They have had their lunch at twelve._____
6.The workers have repaired the machines just now._____
7.You have waited here since two hours._____