write "on" or "in" alternative lines？

[on the way]

Write "on" the alternative lines or write "in" the alternative lines ? Of the two expressions , whcih is the correct way of speaking? Any response will be much appreciated.Thank you all.

 

[5jj]

Write on alternate lines.

 

[Route21]

As an NES but not an English specialist/teacher:

I would write "on" alternate lines (rather than "in") to leave space for a teacher to annotate any necessary corrections.

Hope this helps
R21

 

[Tdol]

As an NES but not an English specialist/teacher:

I would write "on" alternate lines (rather than "in") to leave space for a teacher to annotate any necessary corrections.

Hope this helps
R21

So would I.