Ответ:

  1. When on the street, 19) look both ways before crossing.
  2. When on the bus, don’t 20) talk to the driver.
  3. When you enter the bus, don’t 21) push others.
  4. When on the bus, don’t 22) lean out of the window.
  5. When going to school, 23) walk on the pavement.
  6. When you ride your bike, 24) wear a bicycle helmet.

Ответ: 19 — look; 20 — talk; 21 — push; 22 — lean; 23 — walk; 24 — wear.