Final answer:
The correct spelling in the sentence is 'It's' instead of 'Its'.
Step-by-step explanation:
The correct spelling of the word in the sentence is 'It's' instead of 'Its'. The word 'It's' is a contraction of 'It is' or 'It has'. Contraction is a shortened form of two words where an apostrophe is used to combine them. In this case, 'It's' indicates possession, meaning that the reward belongs to someone. Therefore, the corrected choice is:
It's a wonderful reward for their generous contributions.
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