17.听第10段材料,回答第17至20题.
17.How long will the shortest summer English course last?
A.Two weeks.
B.Four weeks.
C.Six weeks.
18.How can the teachers know that their students have made progress?
A.By offering them an American lifestyle.
B.By providing books and materials.
C.By giving them weekly tests.
19.What is the most interesting part of the course?
A.Living with an American family.
B.Taking a trip to Hollywood.
C.Going to various places.
20.What must you do first if you want to take part in the course?
A.Pay for the course in advance.
B.Choose an American family.
C.Ask for more information.