What does this phrase mean: "in good time"?

[Oana]

Test No. incompl/advan-13 "Time Expressions (1)", question 6

I always like to get to an appointment in ......... time.

(a) good
(b) best
(c) fine
(d) clear

Test No. incompl/advan-13 "Time Expressions (1)", answer 6

I always like to get to an appointment in good time.

Correct answer: (a) good
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Could you please explain why this is the correct answer?

[Alan]

This means so that you have time before an appointment starts and you are not in a rush or late.
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