Teachers often use simple examples to _______ language points that are _______ the students.

If our product ____ unsatisfactory within 7 days in any way, you can take it back.

Go and see that play. I______ you'll enjoy it.

 The professor________ the perfect return of Shenzhou 7 in 2008______ “the most exciting thing in history” in his speech.

Students are often warned that anyone who leaves the classroom at night must remember to _____ all the lights, or he will be fined.