Why "keep up" and not "upkeep"?

[katz]

English Grammar Tests, Elementary Level

ESL/EFL Test #86 "Common English Errors (2)", question 8

I've been so busy with new clients that I hired new staff just to ..........

(a) upkeep
(b) keep up
(c) keep
(d) persist

English Grammar Tests, Elementary Level

ESL/EFL Test #86 "Common English Errors (2)", answer 8

I've been so busy with new clients that I hired new staff just to keep up.

Correct answer: (b) keep up

Your answer was: incorrect
I've been so busy with new clients that I hired new staff just to upkeep.
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why keep up and not upkeep, thanks.

katz

[Alan]

Hi,

There are two constructions: keep up is a phrasal verb

upkeep is a noun

Keep up means maintain/continue with the same standard/rate/speed as in:

If you have been successful, you want to continue at the same level and keep up your high standards.

Upkeep means costs of paying for maintenance as in:

Owners of very large historic houses usually open them to the public so that the income can pay for the upkeep of the buildings.

Alan
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