19 ADULT SUPERVISION REQUIRED Look at the notice above. What does the notice mean? A. Children must be accompanied by their parents. B. Everybody must supervise the children. C. Adult must supervise everybody. D. Parents must be supervised. 20. Complete the dialogue with the suitable expression. Linda : "Why are you so sad?" Oscar : "I lost my ruler." Linda : "Well, you ... things back to their proper place so you can find them easily Oscar : "I guess you're right." A. should return C. must find B. should wash D. must use 21. Students ... to the teacher if they want to learn. A. mustn't listen C. must listen B. mustn't stop D. must stop 22. You ... the question carefully before you write the answer. A. must read C. mustn't read B. must believe D. mustn't believe 23. If you want to be healthy, you ... a lot of fruits and vegetables. A. must not lock C. must lock D. must eat B. must not eat​