----- Nội dung dịch tự động từ ảnh ----- 17. I only came up the stairs because the lift wasn't working. If........ 18. He didn't know how thin the ice was, so he was walking on it quite confidently. If....... 19. She looks very worried because she hasn't heard from him. If....... 20. I have been studying hard for the exam for two weeks, so I feel very tired. If......
