As-needed or as-required

[Guest]

Test No. incompl/advan-45 "At the Office (1)", question 7

It's not worth paying for an annual service when you can simply call the supplier on an as-......... basis.

(a) needed
(b) noted
(c) called
(d) told

Test No. incompl/advan-45 "At the Office (1)", answer 7

It's not worth paying for an annual service when you can simply call the supplier on an as-needed basis.

Correct answer: (a) needed

Your answer was: correct
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The structur "as-needed" and even with hyphen makes me confused.
Are there any other words with "as-..."?
What would be a synonym for "as-needed"?

[Alan]

This means the same as as-required.
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English as a Second Language
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