Meaning of "drop me a line"

[Jojo]

Test No. express/elem-3 "Take it easy", question 7

Don't forget to drop me a line when you're away.

(a) telephone me
(b) call me
(c) write to me
(d) send me a telegram

Test No. express/elem-3 "Take it easy", answer 7

Don't forget to write to me when you're away.

Correct answer: (c) write to me

Your answer was: incorrect
Don't forget to telephone me when you're away.
_________________________

why is it incorrect?

Jojo

[Alan]

This means write me (a line).
_________________
English as a Second Language
You can read my ESL story A day in the life of a parliamentary candidate

[Mike]

Strictly speaking this might have been where the phrase came from but it's fairly informal so people wouldn't take you that litterally.
If someone said that to you they wouldn't be too surprised if you were to call, sms/text, email, etc.

[Alan]

Hi,

I think you should take it literally because that's exactly what it means - write me (a line). If you were going to use other forms of communication, you would say:

Email me/Phone me/Text me and so on, wouldn't you?

Alan
_________________
English as a Foreign Language
You can read my EFL story French or English?