What does this phrase mean: "Keep it up"?

[hien]

Test No. incompl/inter-72 "How to encourage", question 2

I must congratulate you on your efforts. ......... it up!

(a) Continue
(b) Take
(c) Keep
(d) Hold

Test No. incompl/inter-72 "How to encourage", answer 2

I must congratulate you on your efforts. Keep it up!

Correct answer: (c) Keep
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my answer is b is it correct?

[Mosteque]

Is it really???????
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obsequium amicos, veritas odium parit

[Torsten]

OK, I see what you mean. The correct answer is Keep it up which happens to be option c rather than b. And of course that's what Alan meant.
So once again, Keep it up! is the correct answer.

TOEIC listening, photographs: The market