TOEFL Ibt

6 yıl önce

Hello dear teachers, I hope to get your answers)))
I am preparing for TOEFL exam and I am using Longman book I found a question which is a bit complicated to me to understand
Page 22 - Horatio Alger was the author of more thab 100 books for boys in the second half of the nineteenth century that focused on the theme.....
and now the question - the word ''that '' refers to
1. author
2.books
3.boys
according to the answers of the book the correct answer is ''book'', but as I know 'that' refers to singular, for example, Yesterday I found a book that I lost.
and many questions we can see in this book that the word 'that' refers to plural noun, I am thinking maybe in this case 'that' and 'which' are the same, but how we can understand.
since school I know that  the ''that'' is always singular, but know i am confused