100. Scarcely...when 

It is wrong to use than instead of when in these sentences. 

• Incorrect: Scarcely had I reached the station than the train steamed out. 

• Correct: Scarcely had I reached the station when the train steamed out. 

When scarcely begins the sentence, the auxiliary had must come immediately after it. 

• Incorrect: Scarcely I had solved one problem when another cropped up.

 • Correct: Scarcely had I solved one problem when another cropped up. 

• Correct: I had scarcely solved one problem when another cropped up.