BOOKSCHOOSE THE WORD WHOSE UNDERLINED PART IS PRONOUNCED DIFFERENTLY...

15. - TONG HOP BAI TAP TRAC NGHIEM TU LUAN TIENG ANH LOP 12 UNIT 11 BOOKS CO DAP AN
TONG HOP BAI TAP TRAC NGHIEM TU LUAN TIENG ANH LOP 12 UNIT 11 BOOKS CO DAP AN

15. Since their appearance, books are a previous ________ of knowledge and pleasure.

a. source

b. pile

c. amount

d. sum