English expression on line

[Deya]

ESL/EFL Test "At the Office (1)", question 6

If the managers want to stay employed, they will have to learn how to stay on ......... of their jobs.

(a) summit
(b) top
(c) head
(d) line

ESL/EFL Test "At the Office (1)", answer 6

If the managers want to stay employed, they will have to learn how to stay on top of their jobs.

Correct answer: (b) top

Your answer was: incorrect
If the managers want to stay employed, they will have to learn how to stay on line of their jobs.
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Hi,
Why 'on line' here is not correct?

Deya

[Alan]

Hi Deya,

The expression on top of your job suggests you know exactly what you are doing and are in control. On line refers to using the internet.

Alan
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English as a Second Language
You can read my ESL story Have a Break!