Yesterday i bought a book.Books are not very expensive.请问为什么后一个book要加S.快.急

I bought a c- shirt yesterday I bought a pen yesterday.画a pen I bought her a bike yesterday.(改为同义句) I bought a bike ____ _____yesterday. I bought ___(me) a useful dictionary yesterday. I bought a good English Chinese Dictionary yesterday. look! I have bought a digital camera yesterday.是否正确? I bought a bike yesterday 怎么变同义句 I bought a can of cola yesterday.改为一般疑问句 I bought a ticket_____F1 yesterday(填介词） Yesterday,I bought a pizza __20 Yuan in Pizza Hut she bought me a pen yesterday→I（）（）（）（）yesterday I bought a book of cartoons yesterday.对划线部分提问 yesterday画线了 yesterday i bought a book.the book is really hard to understand(合并为一句)yesterday i bought a book______ _______ really hard to understand books,i,these,bought,yesterday,are,the 同义句：Tom bought a pen yesterday. Jack bought a pen yesterday,too.Tome bought a pen yesterday.___ __Jack.()I believe Shanghai is ___most beautiful city in China.A.the second B.second C.a secong D.the first This is _____ new dress I bought yesterday.A a B the 请问该选哪一个? He said ,“I bought a new bike yesterday. ----He said he had bought a new bike the day before.宾语从句中yesterday为何变为the day before? I bought my mother a present yesterday.转换成被动语态