4. Stop talking or you won't understand the lesson.
A. If you don't stop talking, you won't understand the lesson.
B. If you don't stop talking, you wouldn't understand the lesson.
C. If you hadn’t stopped talking, you wouldn’t understand the lesson.
D. If you hadn't stopped talking, you wouldn't have understood the lesson.
5. If the homework is difficult, I will ask you for help.
A. Unless the homework is easy, I won't ask you for help.
B. Unless the homework is difficult, I will ask you for help.
C. Unless the homework is easy, I will ask you for help.
D. Unless the homework isn't difficult, I won't ask you for help.
6. I'll let you borrow the book but you must promise to return it next week.
A. If you promise to return the book, I let you borrow it.
B. If you promised to return the book, I'll let you borrow it.
C. If you promise to return the book next week, I'll let you borrow it.
D. If you promise to return the book next week, I won't let you borrow it.