評論
打印
聽錄音，準確填出劃線部分的單詞或詞組，點擊填空答案，顯示正確答案！
Scientists spend years on research, _ their findings, and these findings are examined by other scientists. That’s how we learn. Like climbing a mountain, we _ three feet and fall back two. It’s a process filled with _ ,but somehow we keep moving ahead.
