HAVE YOU FOUND THE PEN ______ YOU LOST

43. - File thứ 4: de_kiem_tra_lop_11-_sach_cu-_u8-9-10_311201817
File thứ 4: de_kiem_tra_lop_11-_sach_cu-_u8-9-10_311201817
43. Have you found the pen ______ you lost? A. who B. where C. which D. when