43. switches

　　[點撥]空格前是the unseen，可見空格為名詞。前面的句子交代了有些開關是可見的，有些是不可見的，所以這里應該是不可見的開關switches。

　　44. We know the train will take one of the tracks leading out, but we have no idea which one

　　[聽音關鍵詞]know，train，take tracks，no idea，which one

　　45. When we think about the future of the universe, we can see our "track" many billions of years into the future

　　[聽音關鍵詞]think about，future of universe，see track，billions

　　46. The goal of science is to reduce the vagueness at the decision points and find the true road that will be followed

　　[聽音關鍵詞]goal of science，reduce vagueness，find true road