Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 23 to 27.

The relationship between students and teachers is less formal in the USA than in many other countries. American students do not stand up when their teachers (23) _____ the room. Students are encouraged to ask questions during class, to stop in the teacher's office for extra help, and to phone if they are absent. Most teachers (24) _____ students to enter class late or leave early if necessary. (25) _____ the lack of formality, students are still expected to be polite to their teachers and classmates.

When students want to ask questions, they usually (26) _____ a hand and wait to be called on. When a test is being given, talking to a classmate is not only rude but also risky. Most American teachers consider that students who are talking  to each other (27) _____ a test are cheating.

Question 27

A. in

B. when

C. while

D. during