After many experiments and much thought, Beijerinck reported, in 1898, that (1) it was a “live fluid” that caused the tobacco disease.
の、(1)の it と 同じ用法を下記から選ぶ問題で、
(a) It's over 200 miles from London to Manchester. (b) It was Jane who paid for the meal yesterday. (c) It seems that no one really knows where he's gone. (d) “What should I do with the key?” “Oh just leave it on the table.”