What does clockwork mean?

[Nasreddin]

Test No. incompl/inter-78 "Tick Tock", question 4

You can always be sure that there'll be a delivery today as the service is as regular as clock..........

(a) time
(b) task
(c) job
(d) work

Test No. incompl/inter-78 "Tick Tock", answer 4

You can always be sure that there'll be a delivery today as the service is as regular as clockwork.

Correct answer: (d) work

Your answer was: incorrect
You can always be sure that there'll be a delivery today as the service is as regular as clockjob.
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What does it mean?
What the difference betweem clock?

[Torsten]

Clockwork is the machinery that makes a clock run and it has to be very precise and reliable.

The word clockjob does simply not exist.
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Test Of English for International Communication
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